Adding ansible_shell_type and basic environment construction on it

Previously we assumed the shell on the target systems were 'sh'-
compliant when formatting environment variables preceding command
strings. This patch corrects that by basing the target shell type
on the DEFAULT_EXECUTABLE setting, which can be overridden on a
per-host basis using the inventory variable 'ansible_shell_type'.

Fixes #7352

docsite/rst/intro_inventory.rst

@@ -200,6 +200,8 @@ mentioned::
       Connection type of the host. Candidates are local, ssh or paramiko.  The default is paramiko before Ansible 1.2, and 'smart' afterwards which detects whether usage of 'ssh' would be feasible based on whether ControlPersist is supported.
     ansible_ssh_private_key_file
       Private key file used by ssh.  Useful if using multiple keys and you don't want to use SSH agent.
+    ansible_shell_type
+      The shell type of the target system. By default commands are formatted using 'sh'-style syntax by default. Setting this to 'csh' or 'fish' will cause commands executed on target systems to follow those shell's syntax instead.
     ansible_python_interpreter
       The target host python path. This is useful for systems with more
       than one Python or not located at "/usr/bin/python" such as \*BSD, or where /usr/bin/python

lib/ansible/runner/__init__.py

@@ -287,6 +287,10 @@ class Runner(object):
     def _compute_environment_string(self, inject=None):
         ''' what environment variables to use when running the command? '''
 
+        shell_type = inject.get('ansible_shell_type')
+        if not shell_type:
+            shell_type = os.path.basename(C.DEFAULT_EXECUTABLE)
+
         default_environment = dict(
             LANG     = C.DEFAULT_MODULE_LANG,
             LC_CTYPE = C.DEFAULT_MODULE_LANG,
@@ -301,6 +305,9 @@ class Runner(object):
 
         result = ""
         for (k,v) in default_environment.iteritems():
+            if shell_type in ('csh', 'fish'):
+                result = "env %s=%s %s" % (k, pipes.quote(unicode(v)), result)
+            else:
                 result = "%s=%s %s" % (k, pipes.quote(unicode(v)), result)
         return result