Add simple helper function for client construction

Often times you don't want to take advantage of all the flexibility, you
simple want the basic works-like-it-should thing. Add a warpper around
get_legacy_client to do tht one thing.

Change-Id: I086dc4a8e762d4e8e56e01cabe2386577f2ceec8

README.rst

@@ -319,3 +319,34 @@ with - as well as a consumption argument.
   options = parser.parse_args()
 
   cloud = cloud_config.get_one_cloud(argparse=options)
+
+Constructing OpenStack Client objects
+-------------------------------------
+
+If all you want to do is get a Client object from a python-*client library,
+and you want it to do all the normal things related to clouds.yaml, `OS_`
+environment variables, a hepler function is provided.
+
+::
+
+  import argparse
+
+  from novaclient import client
+  import os_client_config
+
+  nova = os_client_config.make_client('compute', client.Client)
+
+If you want to do the same thing but also support command line parsing.
+
+::
+
+  import argparse
+
+  from novaclient import client
+  import os_client_config
+
+  nova = os_client_config.make_client(
+      'compute', client.Client, options=argparse.ArgumentParser())
+
+If you want to get fancier than that in your python, then the rest of the
+API is avaiable to you. But often times, you just want to do the one thing.

os_client_config/__init__.py

@@ -12,6 +12,8 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import sys
+
 from os_client_config.config import OpenStackConfig  # noqa
 
 
@@ -30,3 +32,24 @@ def simple_client(service_key, cloud=None, region_name=None):
     """
     return OpenStackConfig().get_one_cloud(
         cloud=cloud, region_name=region_name).get_session_client('compute')
+
+
+def make_client(service_key, constructor, options=None, **kwargs):
+    """Simple wrapper for getting a client instance from a client lib.
+
+    OpenStack Client Libraries all have a fairly consistent constructor
+    interface which os-client-config supports. In the simple case, there
+    is one and only one right way to construct a client object. If as a user
+    you don't want to do fancy things, just use this. It honors OS_ environment
+    variables and clouds.yaml - and takes as **kwargs anything you'd expect
+    to pass in.
+    """
+    config = OpenStackConfig()
+    if options:
+        config.register_argparse_options(options, sys.argv, service_key)
+        parsed_options = options.parse_args(sys.argv)
+    else:
+        parsed_options = None
+
+    cloud_config = config.get_one_cloud(options=parsed_options, **kwargs)
+    return cloud_config.get_legacy_client(service_key, constructor)