Add a __main__ handler, version command

Recently I've been querying what versions of openstacksdk are
installed in various environments, it would be handy to have a quick
way to see what's installed.  This adds a __main__ handler and a
single command "version" to print the full version (with git
reference).

Change-Id: I690f2987740c804735879985d19752c31490c7c9

doc/source/user/index.rst

@@ -13,6 +13,10 @@ The OpenStack SDK is available on
 
    $ pip install openstacksdk
 
+To check the installed version you can call the module with ::
+
+   $ python -m openstack version
+
 .. _user_guides:
 
 User Guides

openstack/__main__.py

@@ -0,0 +1,40 @@
+# Copyright (c) 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import argparse
+import sys
+
+import pbr.version
+
+
+def show_version(args):
+    print("OpenstackSDK Version %s" %
+          pbr.version.VersionInfo('openstacksdk').version_string_with_vcs())
+
+
+parser = argparse.ArgumentParser(description="Openstack SDK")
+subparsers = parser.add_subparsers(title='commands',
+                                   dest='command')
+
+cmd_version = subparsers.add_parser('version',
+                                    help='show Openstack SDK version')
+cmd_version.set_defaults(func=show_version)
+
+args = parser.parse_args()
+
+if not args.command:
+    parser.print_help()
+    sys.exit(1)
+
+args.func(args)

releasenotes/notes/version-command-70c37dd7f880e9ae.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - The installed version can now be quickly checked with ``python -m
+    openstack version``.