Make ansible_pipelining a connection variable

SSH pipelining can be a significant performance improvement, but it will
not work if sudoers is configured to requiretty. With this change, one
could have pipelining enabled in ansible.cfg, but use sudo to turn off
requiretty in a separate play (or task) where pipelining is disabled:

    - hosts: foo
      vars:
          ansible_pipelining: no
      tasks:
        - lineinfile: dest=/etc/sudoers line='Defaults requiretty' state=absent
          sudo_user: root

(Note that sudoers has a complicated syntax, so the above lineinfile
invocation may be too simplistic for production use; but the point is
that a separate play can do something to disable requiretty.)

lib/ansible/playbook/play_context.py

@@ -51,6 +51,7 @@ MAGIC_VARIABLE_MAPPING = dict(
    port             = ('ansible_ssh_port', 'ansible_port'),
    password         = ('ansible_ssh_pass', 'ansible_password'),
    private_key_file = ('ansible_ssh_private_key_file', 'ansible_private_key_file'),
+   pipelining       = ('ansible_ssh_pipelining', 'ansible_pipelining'),
    shell            = ('ansible_shell_type',),
    become           = ('ansible_become',),
    become_method    = ('ansible_become_method',),
@@ -133,6 +134,7 @@ class PlayContext(Base):
     _shell            = FieldAttribute(isa='string')
     _ssh_extra_args   = FieldAttribute(isa='string')
     _connection_lockfd= FieldAttribute(isa='int')
+    _pipelining       = FieldAttribute(isa='bool', default=C.ANSIBLE_SSH_PIPELINING)
 
     # privilege escalation fields
     _become           = FieldAttribute(isa='bool')
@@ -427,7 +429,7 @@ class PlayContext(Base):
         '''
 
         #FIXME: remove password? possibly add become/sudo settings
-        for special_var in  ['ansible_connection', 'ansible_ssh_host', 'ansible_ssh_pass', 'ansible_ssh_port', 'ansible_ssh_user', 'ansible_ssh_private_key_file']:
+        for special_var in  ['ansible_connection', 'ansible_ssh_host', 'ansible_ssh_pass', 'ansible_ssh_port', 'ansible_ssh_user', 'ansible_ssh_private_key_file', 'ansible_ssh_pipelining']:
             if special_var not in variables:
                 for prop, varnames in MAGIC_VARIABLE_MAPPING.items():
                     if special_var in varnames:

lib/ansible/plugins/action/__init__.py

@@ -149,7 +149,7 @@ class ActionBase:
         if tmp and "tmp" in tmp:
             # tmp has already been created
             return False
-        if not self._connection.has_pipelining or not C.ANSIBLE_SSH_PIPELINING or C.DEFAULT_KEEP_REMOTE_FILES or self._play_context.become_method == 'su':
+        if not self._connection.has_pipelining or not self._play_context.pipelining or C.DEFAULT_KEEP_REMOTE_FILES or self._play_context.become_method == 'su':
             # tmp is necessary to store the module source code
             # or we want to keep the files on the target system
             return True
@@ -367,7 +367,7 @@ class ActionBase:
             remote_module_path = self._connection._shell.join_path(tmp, module_name)
 
         # FIXME: async stuff here?
-        #if (module_style != 'new' or async_jid is not None or not self._connection._has_pipelining or not C.ANSIBLE_SSH_PIPELINING or C.DEFAULT_KEEP_REMOTE_FILES):
+        #if (module_style != 'new' or async_jid is not None or not self._connection._has_pipelining or not self._play_context.pipelining or C.DEFAULT_KEEP_REMOTE_FILES):
         if remote_module_path:
             self._display.debug("transferring module to remote")
             self._transfer_data(remote_module_path, module_data)
@@ -385,7 +385,7 @@ class ActionBase:
         # FIXME: all of the old-module style and async stuff has been removed from here, and
         #        might need to be re-added (unless we decide to drop support for old-style modules
         #        at this point and rework things to support non-python modules specifically)
-        if self._connection.has_pipelining and C.ANSIBLE_SSH_PIPELINING and not C.DEFAULT_KEEP_REMOTE_FILES:
+        if self._connection.has_pipelining and self._play_context.pipelining and not C.DEFAULT_KEEP_REMOTE_FILES:
             in_data = module_data
         else:
             if remote_module_path: