packaging: stricter FQDN validation

common_utils.getConfiguredIps now returns only Ips configured on
non loopback devices.

engine_validators.validateFQDN now tolerates that the FQDN provided
could not be resolved through a DNS but just only by /etc/hosts.
However, if the FQDN is resolved by DNS, it has also to reverse
resolve the ip address provided by the DNS.

engine-setup doesn't accept anymore a FQDN that doesn't pass the
validation, avoiding failures at later stages.

Change-Id: I512446c80dfa9c83adb179a445bfae82736d403f
Bug-Url: https://bugzilla.redhat.com/948311
Bug-Url: https://bugzilla.redhat.com/928667
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>