Fix dns search domain on upgrade from 5.0

Includes testing for sync dns fix. This hook
applies when /etc/resolv.conf domain does not
match content of /etc/fuel/astute.yaml. If
the values do not coincide, DNS_DOMAIN and
DNS_SEARCH are replaced with the domain value
of /etc/resolv.conf.

Change-Id: Ida11df222eeeb59635d1ec3d95303db8a5ebaa8b
Closes-Bug: #1355149