Make default extension path relative to pybasedir
Make default extension path relative to pybasedir

Load extensions from the trove base dir regardless of the current working
directory.

Closes-Bug: 1316195
Change-Id: I7f75998a357d1fb2033ed944c552fd856c2f2939

fabian4/trove,redhat-openstack/trove,zhujzhuo/openstack-trove,cp16net/trove,zhangg/trove,changsimon/trove,openstack/trove,fabian4/trove,zhujzhuo/openstack-trove,hplustree/trove,redhat-openstack/trove,changsimon/trove,zhujzhuo/openstack-trove,mmasaki/trove,cp16net/trove,fabian4/trove,redhat-openstack/trove,zhangg/trove,openstack/trove,mmasaki/trove,hplustree/trove,mmasaki/trove,changsimon/trove,cp16net/trove