Move trove to plugin

Also adds an is_trove_enabled() function to prepare for an upcoming
change in is_service_enabled().

Change-Id: I404e2230602383916f9a717a3d86f6009a1ee4bd
Begin is_service_enabled() cleanup

This lays the groundwork to convert the special cases in the
is_service_enabled() function to call individual functions declared by
the projects.  This allows projects that are not in the DevStack repo
and called via the extras.d plugin to handle an equivalen service alias.

Change-Id: I4879ec51287088f471df867b96e0531bd58908e6
Clean up Glance service checks

Add is_glance_enabled() to lib/glance to enable removing the 'glance'
special-case in the is_service_enabled() function itself.

TODO: remove the glance test from is_service_enabled() after a transition period

Change-Id: I7f1b1b20b2f7f525e4eb820d4e25af603e45bd12
Clean up Ceilometer service checks

Add is_ceilometer_enabled() to lib/ceilometer to enable removing the 'ceilometer'
special-case in the is_service_enabled() function itself.

TODO: remove the ceilometer test from is_service_enabled() after a transition period

Change-Id: Ib3d4eb39f71dc6c2aa6ae58e11ce687ca70d452b
Clean up Cinder service checks

Add is_cinder_enabled() to lib/cinder to enable removing the 'cinder'
special-case in the is_service_enabled() function itself.

TODO: remove the cinder test from is_service_enabled() after a transition period

Change-Id: I6079ba253517d5418f8d193a22d390851696b342
Clean up Swift service checks

Add is_swift_enabled() to lib/swift to enable removing the 'swift'
special-case in the is_service_enabled() function itself.

TODO: remove the swift test from is_service_enabled() after a transition period

Change-Id: I129744a1057fc490890ba9f145b83258a3c4af4a
Clean up Nova service checks

Add is_nova_enabled() to lib/nova to enable removing the 'nova'
special-case in the is_service_enabled() function itself.

TODO: remove the nova test from is_service_enabled() after a transition period

Change-Id: I565b12c54dc5bab52f00f8376b10020123e6ad83
Merge branch 'trove-plugin' into dt-test
Merge branch 'code-cleanup' into dt-test
Merge branch 'enabled-base' into dt-test
Merge branch 'enabled-cinder' into dt-test
Merge branch 'enabled-glance' into dt-test
Merge branch 'enabled-nova' into dt-test
Merge branch 'enabled-swift' into dt-test
Merge branch 'enabled-ceilometer' into dt-test