db2 support

this patch set makes db2 available as a database backend for ceilometer
it implements the blueprint documented at:
blueprints.launchpad.net/ceilometer/+spec/ibm-db2-support

implements bp ibm-db2-support
Change-Id: I33903fe5ebd02679d5a7adbd79dd2650a52f689a
Merge "db2 support"