Use full path for LOCAL_INSTRUMENT_SOURCE_DIRS

We get fail from running RunThemePickerRoboTests-jacoco because Jacoco
fail to get the source code path to parse the code coverage.

Test step:
1. tapas RunThemePickerRoboTests
2. make -j30 dist (Make sure RunThemePickerRoboTests does not break)
3. make -j30 RunThemePickerRoboTests-jacoco dist
4. See the coverage report
Bug: 147334774

Change-Id: I5a76f99a22b1e230b3b4777e74bd1e68211e9736