minnow.conf: Add CheckMinnowExists
minnow.conf: Add CheckMinnowExists

We need to ensure that we check the poky git hash in the main
minnow.conf.

Signed-off-by: Beth Flanagan <86e3219095765dcc0f6f42aef4bd43803a05b796@intel.com>

denny820909/builder,denny820909/builder,denny820909/builder,denny820909/builder