inspection: Get icons from RHEL and CentOS 7 (RHBZ#1164619).
inspection: Allow /etc/favicon.png to be a symbolic link (RHBZ#1164619).

If /etc/favicon.png is a symbolic link, follow it.

Unfortunately RHEL 7 and Fedora have crappy 16x16 /etc/favicon.png
symlinks in the base distro.  It would be nice to ignore this symlink,
but it's almost impossible to determine if the symlink is part of the
base distro or was added by the user.  (This is a bug in those
distros.)  virt-inspector and virt-mananger both ignore favicons.