refactor db2 get_meter_statistics method to support mongodb and db2

db2 driver for get_meter_statistics method did not work against mongodb
which caused many test cases being skipped. This patch set will fix
that problem also made sure that all statistics functions are supported
by db2 driver against db2 and mongodb database

fixes: bug #1226079

Change-Id: I502aebbab51c51970ddb68641dab89944ce810d4
WSME 0.5b5 breaking unit tests

- fix tests to accept new (accurate) response codes
- wsme doesn't like us sending gettextutils.Message values. pass in
a regular string

Change-Id: Ie9e05edfd542ba1fe8c6fdbeed2daab12cf30caf
Fixes:Bug #1227264
Update requirements

Change-Id: If103fa3d8479956878258be6b7d32f1f63cdfd8a
Merge "refactor db2 get_meter_statistics method to support mongodb and db2"
Merge "Update requirements"
Fix for timestamp precision in SQLAlchemy

This fix adds the PreciseTimestamp custom type to address how
MySQL < 5.6.4 truncates temporal columns to the second:
http://dev.mysql.com/doc/refman/5.6/en/fractional-seconds.html

Change-Id: I9d324d1cb6867cf99e15e2ecdc566dc5f8fef536
Closes-Bug: #1215676