Check version of mojo bootstrap from lacros socket.

This also fixes a bug where sometimes fds are not received and
lacros can't start.

Bug: 1139796
Test: Can run lacros on chromeos via this script
Change-Id: I33f5fae07b377fb7848dc444be7fcb4f8d4a3f46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2483749
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819196}