core: Add snakeyaml dependency

Cloud-Init requires snakeyml in VDS broker,
so adding the dependency to it.

Change-Id: I6bb434c6f7051a457ca51fb7d4c323a90e830931
Bug-Url: https://bugzilla.redhat.com/994129
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>