Let #getUiAutomation return null if UiAutomation fails to connect (3/n)

Now #getUiAutomation returns null if the underlying UiAutomation fails
to connect for targetSdkVersion > R. This gives the caller a chance to
retry and decide when to give up.

Bug: 147785023
Test: presubmit
Change-Id: Ibf201fa042b80c067f2a0c3b0bde23adf9c60546
Merged-In: Ibf201fa042b80c067f2a0c3b0bde23adf9c60546
1 file changed