Improve help strings
Improve help strings

Follow oslo.config style guide for help strings better to create
more consistent help strings:
* Capitalize first word of each help string
* Finish help strings with "."
* Improve wording, capitalization

Change-Id: I8a8832c02f0af955a58080371459ff6edffcb111

magic0704/oslo.db,openstack/oslo.db,openstack/oslo.db,JioCloud/oslo.db,akash1808/oslo.db,varunarya10/oslo.db