packaging: setup: enforce perms on iso domain

previously if an existing directory was specified
for using it as iso domain its ownership and access bits
where untouched.

Now ownership and access bits are enforced.

Change-Id: I3ba820073983e0c32f7e762f0e6f34753528b6e6
Bug-Url: https://bugzilla.redhat.com/1004005
Bug-Url: https://bugzilla.redhat.com/1004395
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>