[res] Fix ObfuscatorTest to run in Blaze sandbox

blaze creates a sandbox with readonly current directory, and
all tests have to use the system temp dir - which this one didn't

Bug: n/a
Test: atest aapt2_tests
Change-Id: Ia5a03ad5c8a4ef594f3c379c4502b976f5c08ac4
1 file changed