Provide keystone CLI man page.

Resolves: bug 1185142
Implements blueprint: clients-man-pages

Provide basic but hopefully useful man page.

shell.rst was merged into and replaced by the man page in HTML docs.

Change-Id: I0a90e4638cc7e4ed9c02c5abd7d84a4079e5f50d
Merge "Provide keystone CLI man page."