smb_provider_client: Refactor calls to DBUS methods.

- Removes duplicated code in calling DBUS methods
- Add helper method that sets up the message and provides all the
  default arguments.

BUG: chromium:757625
Change-Id: I59652da1da2c33a89cdab3a16d80c4b3d95b63d6
Reviewed-on: https://chromium-review.googlesource.com/837722
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525801}
2 files changed