Clean up keystone-manage man page

Several warnings were generated from keystone-manage when
building docs. Also, the options without a description
didn't display correctly in the rendered result.

Also, I added a description for the new db_version subcommand.

To generate the new option list, I ran keystone-manage --help
and copy-pasted the options into the doc.

Change-Id: I1a405ca03d894c9c3e0f6b3bfccc9bcfcce1302d
Merge "Clean up keystone-manage man page"