Use Mount() for SMB share "premount"

Premount is the same as Mount(skip_connect) with no credentials. Change
premount mode to use the regular Mount() D-Bus method so that the
interface and smbprovider can be simplified.

BUG=None

Change-Id: I7deaa33d1fbd0418752ce97e85e0561c6e2180d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1621787
Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Anand Mistry <amistry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661632}
2 files changed