Better error messages if a2enmod/a2dismod are not found

lib/ansible/modules/web_infrastructure/apache2_module.py

@@ -49,6 +49,9 @@ import re
 def _disable_module(module):
     name = module.params['name']
     a2dismod_binary = module.get_bin_path("a2dismod")
+    if a2dismod_binary is None:
+        module.fail_json(msg="a2dismod not found.  Perhaps this system does not use a2dismod to manage apache")
+
     result, stdout, stderr = module.run_command("%s %s" % (a2dismod_binary, name))
 
     if re.match(r'.*' + name + r' already disabled.*', stdout, re.S):
@@ -61,6 +64,9 @@ def _disable_module(module):
 def _enable_module(module):
     name = module.params['name']
     a2enmod_binary = module.get_bin_path("a2enmod")
+    if a2enmod_binary is None:
+        module.fail_json(msg="a2enmod not found.  Perhaps this system does not use a2enmod to manage apache")
+
     result, stdout, stderr = module.run_command("%s %s" % (a2enmod_binary, name))
 
     if re.match(r'.*' + name + r' already enabled.*', stdout, re.S):
@@ -86,4 +92,5 @@ def main():
 
 # import module snippets
 from ansible.module_utils.basic import *
-main()
+if __name__ == '__main__':
+    main()