core: Move animal-sniffer to pluginManagement

Moved animal-sniffer definition from <plugins> to <pluginManagement> so
maven does not download the plugin if the animal-sniffer goal is not
invoked.

Change-Id: I6748886415f8be2ae970b962ec67473dec1729b1
Signed-off-by: Allon Mureinik <amureini@redhat.com>