Mask database user's password in trove logs

Currently passwords are logged in plaintext in trove-api and
trove-taskmanager logs. This fix will mask the passwords in the logs.
Syncing modules log, common.py from rpc  and versionutils from oslo.
common.py requires versionutils.py.

Change-Id:I50deb003d866e85e7c7ec8ab3ce7248d1c005e57
Closes-Bug: #1254914
Corrects help messages in cfg.py

Reasons:
- Few typos.
- Help message sentences not ending with a full-stop(.).

Changes:
- Typos corrected.
- . added to end-of-sentences in help messages.

Change-Id: I29f0d266c9b87d9bf90cd15084ef02699532d79e
Closes-Bug: #1272020
Merge "Mask database user's password in trove logs"
Initial support for single instance Cassandra Database

Reasons
- This code adds ability to create/delete instance
with mongodb service type. No other operations supported.
- Trove should support multiple extensions. One of the is NoSQL support.
Main goal is to add support for Apache Cassandra NoSQL database.

Changes
This code gives ability to create/delete instance
with cassandra datastire type. No other operations supported.

Change-Id: Ib48f6392765af49c2df1447c3df46675825d210f
Implements: blueprint cassandra-db-support