GitLab

Make AndroidShell.InitShell return an exit code.
(infra exit code for infra errors and 'device not found')

Inline CleanShell in InitShell; store --origin internally.
Move gdb port forwarding to StartShell; minor refactoring.

BUG=493900
TEST=Mojo/Mandoline python scripts work as expected. Bots yield purple builds on "device not found" errors.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/1143223005

Cr-Commit-Position: refs/heads/master@{#333186}