vdsm: centralize device limit checking

Device limits are currently checked on case by case bases,
this patch implements call that centralizes the checking

Change-Id: I2712148b670c9f85beaea40a0b2e870d829b2b4b
Signed-off-by: mpolednik <mpoledni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/18047
Reviewed-by: Dan Kenigsberg <danken@redhat.com>