Document the os options config for swift store

Several configuration options were added to the swift store. These
options help python-swiftclient and sometimes glance itself to determine
which swift service to use if multiple services appear in a keystone
catalog. This change adds documentation for the additional options.

Last fix for bug 1037708

Change-Id: Id06d263b73705b06295b730ff68460b22f117e63
Merge remote-tracking branch 'm_src_repo/webob-issue' into build-temp