Add a multibackend list to tempest.conf

A change was made to tempest.conf for volume multibackend. Previously,
tempest used the following, with a limit of 2 backends:
 backend1_name = BACKEND1
 backend2_name = BACKEND2
That was changed to accomodate >2 backends. tempest.conf now uses a comma
separated list:
 backend_names=BACKEND1,BACKEND2,BACKEND3

devstack/lib/cinder uses a comma separated list with "type:backend_name":
 enabled_backends = lvm:BACKEND1,ceph:BACKEND2
This is in order to use scripts in devstack/lib/cinder_backends to setup
devstack basked on "type".

This patch allows parsing of the CINDER_ENABLED_BACKENDS to pass the proper
backend_name to tempest.

Change-Id: I76973c3fad4998a0f9e534fc9f6a271c1923f7b3

lib/tempest

@@ -462,15 +462,26 @@ function configure_tempest {
     fi
 
     # Using ``CINDER_ENABLED_BACKENDS``
+    # Cinder uses a comma separated list with "type:backend_name":
+    #  CINDER_ENABLED_BACKENDS = ceph:cephBE1,lvm:lvmBE2,foo:my_foo
     if [[ -n "$CINDER_ENABLED_BACKENDS" ]] && [[ $CINDER_ENABLED_BACKENDS =~ .*,.* ]]; then
+        # We have at least 2 backends
         iniset $TEMPEST_CONFIG volume-feature-enabled multi_backend "True"
-        local i=1
+        local add_comma_seperator=0
+        local backends_list=''
         local be
+        # Tempest uses a comma separated list of backend_names:
+        #   backend_names = BACKEND_1,BACKEND_2
         for be in ${CINDER_ENABLED_BACKENDS//,/ }; do
-            local be_name=${be##*:}
-            iniset $TEMPEST_CONFIG volume "backend${i}_name" "$be_name"
-            i=$(( i + 1 ))
+            if [ "$add_comma_seperator" -eq "1" ]; then
+                backends_list+=,${be##*:}
+            else
+            # first element in the list
+                backends_list+=${be##*:}
+                add_comma_seperator=1
+            fi
         done
+        iniset $TEMPEST_CONFIG volume "backend_names" "$backends_list"
     fi
 
     if [ $TEMPEST_VOLUME_DRIVER != "default" -o \