Allow blank keystone flavor in glance configs

Blank keystone flavor now allowed in api.pp and registry.pp
Pipeline config logically separate from keystone config (pipeline can
be set even if auth_type is not defined.)
Added rspec tests.

Change-Id: Ic4fbff44242459f504cd14ef18915b2efac2d032
Fixes: bug #1190475
Merge "Allow blank keystone flavor in glance configs"