Add KEY_ID and server for mitaka-staging test repository

Mitaka staging test repository for test-kitchen was
missing KEY_ID which prevented apt-get update to
run successfuly.

Signed-off-by: Ondrej Vasko <ondrej.vaskoo@gmail.com>

tests/pillar/repo_galeracluster.sls

@@ -12,3 +12,5 @@ linux:
         key_server: hkp://p80.pool.sks-keyservers.net:80
       mitaka-staging_PPA:
         source: "deb http://ppa.launchpad.net/ubuntu-cloud-archive/mitaka-staging/ubuntu trusty main"
+        key_id: 8A6844A29F68104E
+        key_server: hkp://p80.pool.sks-keyservers.net:80