STS: Improve robustness of containsDriver()

Bug: 153489569
Test: check containsDriver() against a normal file
Test: check containsDriver() against a file that doesn't exist
Test: check containsDriver() against a file that the caller doesn't have permission to read
Change-Id: Ia31e9c11f84aae3b340b2cbdb5cb24658e577635
1 file changed