Use Android Q compatible external dir

We previously used Environment.getExternalDir to obtain the output dir for the tests. However, since Android Q this method is deprecated and returns an invalid path, leading to errors. Replace this method for context.getExternalDir(null) that return a Q  friendly path.

Test: atest FlickerTests
Bug: 161341377
Change-Id: I5389ac6116b2b74fb19417683dbcfca604ca5b58
3 files changed