Add authentication parameters to SmbProviderClient::Remount

This change adds authentication parameters to SmbProviderClient::Remount
so ChromAD Kerberos shares can be remounted by passing in a user's
username and workgroup.

Bug: chromium:757625
Change-Id: I201a100526cbf1f29188e2b9b7e797c60b929620
Reviewed-on: https://chromium-review.googlesource.com/1098079
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571882}
5 files changed