Adds cinder backup functional tests

Adds new tests to cover cinder backup api as well as the needed
json clients.

xml client will be submitted after bug #1270589 is fixed.

Change-Id: I8d40c58eaf0ccd24abf55a212f1177e61ef0a281
Closes-Bug: 1221335
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 2443399..30e3aa1 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -822,6 +822,9 @@
 # (boolean value)
 #multi_backend=false
 
+# Runs Cinder volumes backup test (boolean value)
+#backup=true
+
 # Is the v1 volume API enabled (boolean value)
 #api_v1=true