Improve hostname module to support systemd in more generic way (#4382)

Now that there is general purpose `Fact` helper to detect if systemd
is active, we would be able to rely on that to apply SystemdStrategy.

Detecting presence of systemd at runtime would be more reliable than
distribution version based heuristics. (e.g., Debian, Ubuntu allows
user to change the default init system, Gentoo allows switching as
well, and so on).

system/hostname.py

@@ -48,6 +48,7 @@ from distutils.version import LooseVersion
 
 # import module snippets
 from ansible.module_utils.basic import *
+from ansible.module_utils.facts import *
 
 
 class UnimplementedStrategy(object):
@@ -94,9 +95,12 @@ class Hostname(object):
         return load_platform_subclass(Hostname, args, kwargs)
 
     def __init__(self, module):
-        self.module   = module
-        self.name     = module.params['name']
-        self.strategy = self.strategy_class(module)
+        self.module       = module
+        self.name         = module.params['name']
+        if self.platform == 'Linux' and Facts(module).is_systemd_managed():
+            self.strategy = SystemdStrategy(module)
+        else:
+            self.strategy = self.strategy_class(module)
 
     def get_current_hostname(self):
         return self.strategy.get_current_hostname()
@@ -512,9 +516,7 @@ class SLESHostname(Hostname):
     platform = 'Linux'
     distribution = 'Suse linux enterprise server '
     distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("12"):
-        strategy_class = SystemdStrategy
-    elif distribution_version and LooseVersion("10") <= LooseVersion(distribution_version) <= LooseVersion("12"):
+    if distribution_version and LooseVersion("10") <= LooseVersion(distribution_version) <= LooseVersion("12"):
         strategy_class = SLESStrategy
     else:
         strategy_class = UnimplementedStrategy
@@ -537,65 +539,37 @@ class RedHat5Hostname(Hostname):
 class RedHatServerHostname(Hostname):
     platform = 'Linux'
     distribution = 'Red hat enterprise linux server'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class RedHatWorkstationHostname(Hostname):
     platform = 'Linux'
     distribution = 'Red hat enterprise linux workstation'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class CentOSHostname(Hostname):
     platform = 'Linux'
     distribution = 'Centos'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class CentOSLinuxHostname(Hostname):
     platform = 'Linux'
     distribution = 'Centos linux'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class ScientificHostname(Hostname):
     platform = 'Linux'
     distribution = 'Scientific'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class ScientificLinuxHostname(Hostname):
     platform = 'Linux'
     distribution = 'Scientific linux'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class OracleLinuxHostname(Hostname):
     platform = 'Linux'
     distribution = 'Oracle linux server'
-    distribution_version = get_distribution_version()
-    if distribution_version and LooseVersion(distribution_version) >= LooseVersion("7"):
-        strategy_class = SystemdStrategy
-    else:
-        strategy_class = RedHatStrategy
+    strategy_class = RedHatStrategy
 
 class AmazonLinuxHostname(Hostname):
     platform = 'Linux'
@@ -658,7 +632,7 @@ class FreeBSDHostname(Hostname):
 def main():
     module = AnsibleModule(
         argument_spec = dict(
-            name=dict(required=True, type='str')
+            name=dict(required=True)
         )
     )
 
@@ -682,4 +656,5 @@ def main():
                                         ansible_fqdn=socket.getfqdn(),
                                         ansible_domain='.'.join(socket.getfqdn().split('.')[1:])))
 
-main()
+if __name__ == '__main__':
+    main()