Migrate DeviceUtils.EnableRoot to adb_wrapper

Migrate DeviceUtils.EnableRoot to adb_wrapper

The new implemention is simply based on adb.Root, which already
throws an exception when the command is not successful.

BUG=267773
Committed: https://crrev.com/63919c1ae931d28cda16030573cc607ebae76a8a
Cr-Commit-Position: refs/heads/master@{#306401}

[perezju, 2014-12-02 12:12:14]

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

[perezju, 2014-12-02 12:12:15]

This one should be pretty straightforward

[jbudorick, 2014-12-02 15:20:53]

lgtm

[perezju, 2014-12-02 16:09:52]

The CQ bit was checked by perezju@chromium.org

[commit-bot: I haz the power, 2014-12-02 16:10:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/772003002/1

[commit-bot: I haz the power, 2014-12-02 16:57:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-02 16:58:28]

Patchset 1 (id:??) landed as
https://crrev.com/63919c1ae931d28cda16030573cc607ebae76a8a
Cr-Commit-Position: refs/heads/master@{#306401}