Check at startup if a given store exists (#275)

* add check to see if a store exists

tests/startup-test/test.sh

@@ -31,3 +31,6 @@ docker exec kopano_server kopano-cli --list-users
 docker exec kopano_server kopano-admin -l
 docker exec kopano_zpush z-push-admin -a list
 docker exec kopano_zpush z-push-gabsync -a sync
+
+# will print nothing if store exists and fail if it doen't
+docker exec kopano_server kopano-admin --details user1 | grep -q "^Store GUID:"