Manually enable root during test setup

While invoking apexd_host_test in internal branch, I've noticed that for
some reason root get's disabled between test runs. To work around this
issue, let test setup to manually enable adb root.

Test: atest apexd_host_test
Test: apex_rollback_test
Change-Id: Iab021fa78b49d402a041aaef125cd9af731f65fb
Ignore-AOSP-First: resolving internal merge conflicts
2 files changed