Fixed two bugs with lkgr finder
Fixed two bugs with lkgr finder

This change attempt to fix two cases where lkgr_finder may break.
1. A build failed before 'got_revision' property was there. If we allow fallback
to 'revision' then non-chromium rev or svn rev may be used.
2. A build is running but 'got_revision' does not present. If we allow fallback
to 'revision' then we may get svn rev.

BUG=337035
R=szager@chromium.org, agable@chromium.org

Review URL: https://codereview.chromium.org/481343003

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra