Add presubmit repo hook to check license headers in luni/ojluni

This CL adds two hooks for checkstyle tool that will ensure that java
files under luni/ and ojluni/ directories do not contain undesired
licenses: ojluni/ generally must not have APACHE-licensed files, and
luni/ must not have GPL-licensed files.

This will help to prevent errors when wrong license is added
accidentally.

Bug: 38121042
Test: run ${ANDROID_BUILD_TOP}/tools/repohooks/pre-upload.py -- script fails as expected
Test: Add GPL license in the header of java file under luni/, commited it and tried to
      upload such change -- failed to upload as expected
      Did the same thing but for Apache license and java file under
      ojluni/ -- same results as expected
Change-Id: Ia15091e1cff1e76eda9c2708345d2d09cdc5b7f3
3 files changed