[Android] Speculative fix for DeviceUtils.EnableRoot issues.

[Android] Speculative fix for DeviceUtils.EnableRoot issues.

Several bots occasionally fail commands immediately following calls to
DeviceUtils.EnableRoot with "device not found" errors. I think this may
be because adb wait-for-device can come back before the device is
completely available. Switching to WaitUntilFullyBooted should ensure
that the device has returned to a usable state (or is actually gone).

BUG=493900
Committed: https://crrev.com/a95af720637c609f33ed76d89d658041f354a222
Cr-Commit-Position: refs/heads/master@{#333046}

[jbudorick, 2015-06-05 03:27:27]

jbudorick@chromium.org changed reviewers:
+ perezju@chromium.org

[perezju, 2015-06-05 08:28:12]

lgtm

[jbudorick, 2015-06-05 13:49:04]

The CQ bit was checked by jbudorick@chromium.org

[commit-bot: I haz the power, 2015-06-05 13:49:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1167903006/1

[commit-bot: I haz the power, 2015-06-05 14:49:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-05 14:50:42]

Patchset 1 (id:??) landed as
https://crrev.com/a95af720637c609f33ed76d89d658041f354a222
Cr-Commit-Position: refs/heads/master@{#333046}