Specify DB URL on command-line for schema_diff.py

The exising schema_diff code had the DB URL format hard-coded which made it
difficult to work with since different environments with have different
user/password configurations.

A more flexible way to handle this, is to have the DB URL specified directly
on the command-line.

Change-Id: I313bb616e439072e007c886a7f131efc6a61f6df
add comment about why snapshot/backup have no lock check

This comment is intended to reduce further confusion about why a
lock check hasn't been implemented for snapshot and backup.

Change-Id: I8d89ca7b15d6713221af2d0535f9ed338ca70612
Related-Bug: #1314741
Use pool/volume_name notation when deleting RBD volumes

the rbd command supports two methods for specifying a pool name:
the "-p" flag, and using the volume name notation "pool_name/volume_name"
The latter method supercedes the former, so to guard against slashes
in the volume name confusing things, always use the path notation

Change-Id: Ie79ae10b0fafefd85dea8e38cd24da0941b38bee
Closes-Bug: 1306285
Merge "add comment about why snapshot/backup have no lock check"
Merge "Specify DB URL on command-line for schema_diff.py"
Merge "Use pool/volume_name notation when deleting RBD volumes"