Move gettextutils installation in tests to core

gettextutils.install was done in tests/__init__.py, but this was
not consistent with how test environment setup is done. We have
code to set up the environment in core.py, so other environment
setup should be there. Also, this makes tests/__init__.py cleaner.

Change-Id: I762c8fa715e9c6ec26722fcd9b0ba0f9d613cb43
Merge "Move gettextutils installation in tests to core"