vts: fix TryDifferentGovernors in Power hal test

The test should return when it cannot open cpu governor files
BUG: 62138092

Test: build sdk_gphone_x86-userdebug, launch emulator,
run test: run vts -m VtsHalPowerV1_0Target
The test should all pass.

Change-Id: I3b47261e9525b6a04e995dac1ad63d9cc088b004
1 file changed