Parametrize rndc key algorithm

Currently there is no consistent way to set rndc key algorithm
in both designate and bind. This patch fixes this.

Change-Id: Ib6ad9142f843aafce41e60de79d77e8eb315d7e8
diff --git a/designate/server/backend/bind.yml b/designate/server/backend/bind.yml
index 2b40424..c057eb7 100644
--- a/designate/server/backend/bind.yml
+++ b/designate/server/backend/bind.yml
@@ -1,15 +1,18 @@
 parameters:
+  _param:
+    designate_bind9_rndc_algorithm: hmac-sha512
   designate:
     server:
       backend:
         bind9:
           rndc_key: "${_param:designate_bind9_rndc_key}"
+          rndc_algorithm: "${_param:designate_bind9_rndc_algorithm}"
   bind:
     server:
       key:
         designate:
           secret: "${_param:designate_bind9_rndc_key}"
-          algorithm: hmac-sha512
+          algorithm: "${_param:designate_bind9_rndc_algorithm}"
       allow_new_zones: true
       query: true
       control:
@@ -33,4 +36,4 @@
       key:
         designate:
           secret: "${_param:designate_bind9_rndc_key}"
-          algorithm: hmac-sha512
+          algorithm: "${_param:designate_bind9_rndc_algorithm}"