Checking for LUCI_CONTEXT is not enough. To use local auth, the
stored config must be valid and have a default account id.

Bug: 1018069
Change-Id: I5bbe880cc217a06ae0e1ae8d7e00ef09502af6a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1888211Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>