core: fix cloud-init userData content

some changes needed to comply with cloud-init userData requirements:

* add needed #cloud-config header to userData file:
this fix all commands sent in userData like timezone and cloud-init
configuration settings

* move password from metaData to userData
root password parameter should be in userData,
and not in metaData.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1004829

Change-Id: I4642aaf1d9349ebbe82b7c77e562ad5ca19ca3ee
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>