Improve help strings

The help strings where rather inconsistent in their usage
of '.' and capitalization. Now all strings end with a "." and
are capitalized.

This leads to output like:
--alarm_ids <ALARM IDS>
                        List of alarm id Required.

Note the missing period before "Required".

Change-Id: I5edf0d4584b7f01d941068818c9dd0d17043ffaa
test_url_generation_with_proxy: do not use contextlib.nested()

This method does not exist in Python 3, use the "@mock.patch.object" decorator
instead.

Change-Id: Ic45fea1553320c61be284a9397b54fd32f7d30ef
Fix a typo in a comment in v2 client

Change-Id: I835af00af62046e9a391a08e675bc6eeb7267824
Merge "Fix a typo in a comment in v2 client"
Python 3 compatibility

* add Python 3 classifiers
* require at least keystoneclient 0.6.0, since it is the first version that
  works with Python 3.

Change-Id: I631c94d6efa0f7d58ade4a8e044c87558ee58c15
Merge "Improve help strings"
Merge "Python 3 compatibility"