Changed isRoboletricTest() to check against VM.

The original isRobolectricTest() used Build.os.HARDWARE, but sometimes
the Robolectric environment isn't initialized, so we test against the
VM which is a bit more robust.

Bug: 346864770
Flag: TEST_ONLY
Test: tested manually with atest
Change-Id: Ie0c117210e899fe1ddb94f66dae551d44c768915