Begin is_service_enabled() cleanup

This converts 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 equivalent service alias.

* Ceilometer
* Cinder
* Glance
* Neutron
* Nova
* Swift

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

Patch Set 2: Rebased

Change-Id: Ic78be433f93a9dd5f46be548bdbd4c984e0da6e7
diff --git a/exercises/boot_from_volume.sh b/exercises/boot_from_volume.sh
index ed8ba63..7912046 100755
--- a/exercises/boot_from_volume.sh
+++ b/exercises/boot_from_volume.sh
@@ -30,14 +30,12 @@
 # Import common functions
 source $TOP_DIR/functions
 
+# Import project functions
+source $TOP_DIR/lib/cinder
+
 # Import configuration
 source $TOP_DIR/openrc
 
-# Import neutron functions if needed
-if is_service_enabled neutron; then
-    source $TOP_DIR/lib/neutron
-fi
-
 # Import exercise configuration
 source $TOP_DIR/exerciserc