udisks2: support fstab comments to set name and icon

For example, for this /etc/fstab entry

 nfs-server:/path/to/dir  /media/somewhere  nfs4  defaults,users,comment=gvfs.name=Foo\040Bar,comment=gvfs.icon_name=gnome-help 0 0

the name "Foo Bar" and the icon gnome-help is used.

This depends on the glib2 patch from this bug

 https://bugzilla.gnome.org/show_bug.cgi?id=660536



Signed-off-by: David Zeuthen <davidz@redhat.com>