[API] Use of ConfigParser for keystone section

Needed to add this bit of code back, because otherwise we'd have
to register all keystone options in Libra.

Change-Id: Ia8c0877e9b32b7b59728776203bb4cb1d8ec50ce
[admin_api] Fix for bad error message
Show the device name instead of its id when there is no LB attached

Change-Id: I0437c2594f1a1da3d72e26334c226169900d4f6f