CrOS save crostini shared paths to prefs

Once path has been validated, save it to prefs.  Even if the call
to seneschal fails, the path should be saved.

Bug: 878324
Change-Id: Ifdf7270b39031c3c8b4a6cd1fbad5e2005a0f194
Reviewed-on: https://chromium-review.googlesource.com/c/1270557
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598602}
3 files changed