[systemd-devel] [RFC v2] mount: improve DefaultDependencies and use in generator

[Tom Gundersen]

This moves reduces redundancy between systemd core and the fstab-generator, by
improving and relying on the DefaultDependencies logic.

Functional changes:

 * Mount units will no longer Want network.target, only order themselves
   After it.
 * Both monut and swap units will now be WantedBy their backing
device, unless they have the option "noauto".
 * Mount units in the real instance representing mounts that are known
   to be mounted in the initrd (i.e., /usr and anything marked with
   "x-initrd.mount") will no longer conflict with unmount.target.