Remove obsolete config options in libvirt plugin

The libvirt detection plugin has been using the 'sql_connection'
configuration value from nova.conf, but while that is still present in
DevStack, it has been deprecated in OpenStack as of Havana.  Also, it
is completely unused, a relic of an earlier version of the detection
plugin.

Furthermore, the 'identity_uri' value only seems to exist in the
DevStack nova.conf, and is not present in OpenStack.  This value is now
built using auth_* configuration values, which exist in both.

Change-Id: I53269c16773013df213f2acbe02c0e1028d7e81b
Merge "Remove obsolete config options in libvirt plugin"
Revert change in libvirt plugin identity API ver.

The libvirt detection plugin uses an identity URI to fetch information
on provisioned instances.  It was recently changed to v3, but v3
may not work properly on DevStack, so revert to v2.0.

Change-Id: Ic35d99989a936bcb1f8aa2e7169dfd089df51824
Removing dependency on hard-coded version file

Change-Id: Ib291f17d879379125a242136d36fe9abfda7eece
Merge commit '9e61e3ab2c1e87b676735a56c2b2b2179086fa8a'