adds two new plugins that use ansible-connection for persistence (#18572)

* adds new connection plugin `network_cli` which builds on paramiko
* adds new plugin `terminal` used for manipulating network_cli terminals
* adds new field to play_context `network_os` settable as ansible_network_os

This commit adds the plugins necesary to establish a persistent cli connection
to network devices of ssh.  It builds on the paramiko connection plugin
to create a shell environment that will persistent through ansible-connection.
The `newtork_cli` plugin then uses the network_os in the instance of
PlayContext to load the appropriate network OS environment plugin for
handling opening and closing of shells as well as privilege escalation.

lib/ansible/plugins/terminal/__init__.py

@@ -0,0 +1,71 @@
+#
+# (c) 2016 Red Hat Inc.
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+#
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import re
+
+from abc import ABCMeta, abstractmethod
+
+from ansible.compat.six import with_metaclass
+from ansible.errors import AnsibleConnectionFailure
+
+
+class TerminalBase(with_metaclass(ABCMeta, object)):
+    '''
+    A base class for implementing cli connections
+    '''
+
+    terminalprompts_re = []
+
+    terminalerrors_re = []
+
+    ansi_re = [
+        re.compile(r'(\x1b\[\?1h\x1b=)'),
+        re.compile(r'\x08.')
+    ]
+
+    supports_multiplexing = True
+
+    def __init__(self, connection):
+        self._connection = connection
+
+    def _exec_cli_command(self, cmd, check_rc=True):
+        rc, out, err = self._connection.exec_command(cmd)
+        if check_rc and rc != 0:
+            raise AnsibleConnectionFailure(err)
+        return rc, out, err
+
+    def _get_prompt(self):
+        for cmd in ['\n', 'prompt()']:
+            rc, out, err = self._exec_cli_command(cmd)
+        return out
+
+    def on_open_shell(self):
+        pass
+
+    def on_close_shell(self):
+        pass
+
+    def on_authorize(self, passwd=None):
+        pass
+
+    def on_deauthorize(self):
+        pass
+