wam/wash/saltpig: Add domfs, other tweaks.

wam:
* Add wam.jsfs.DOMFileSystem.
* rename jsfs's "opList" to "abilities".
* Treat the "FORWARD" ability special.  If an entry can "FORWARD", then it
  can ONLY forward.  Other listed abilities refer to what the destination
  can do.
* Let remote wam filesystems give themselves a name in their "ready" reply.

wash:
* Hook up wam.jsfs.DOMFileSystem.
* tweak ls output.
* Default mount path to remote filesystem name in mount.chrome.
* Make PATH a real environment variable.

saltpig:
* Hook up wam.jsfs.DOMFileSystem
* Fix public key.

Change-Id: I0ecd10ce71c81e34cc456c63082d261a5e543c59
Reviewed-on: https://chromium-review.googlesource.com/199145
Reviewed-by: Robert Ginda <rginda@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>