Add RootTargetPreparer for explicitly specifying the root dependency

Before, the test gets root implicitly via DeviceSetup which
wasn't intented.

Change-Id: Ib227960223dca1f4b4b73601d1e36ccd93d078e5
Merged-In: I4b86fd5ee31f746942a2bf073a29cb2180a39f27
Test: presubmit
Bug: 330749511

tests/BootImageProfileTest/AndroidTest.xml

@@ -14,6 +14,7 @@
      limitations under the License.
 -->
 <configuration description="Config for BootImageProfileTest">
+     <target_preparer class="com.android.tradefed.targetprep.RootTargetPreparer" />
      <!-- do not use DeviceSetup#set-property because it reboots the device b/136200738.
          furthermore the changes in /data/local.prop don't actually seem to get picked up.
     -->