Fix reboot breaking VR perf tests

Fixes the reboot caused by removing the system installation of VrCore
during the VR perf tests causing the tests to fail due to not being able
to connect to the test server. This was due to the reboot removing the
adb port forwarding that is set up during shared state creation.

The workaround is to manually shut down Telemetry's network controller
before a potential reboot, then starting it back up again afterwards.

Bug: 972221
Change-Id: I34c2fc5731930cfe93202b296957a9d59aa4e1ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1665911
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670584}