Consolidate requirements.txt and test-requirements.txt
Consolidate requirements.txt and test-requirements.txt

- Make test-requirements.txt pull requirements from requirements.txt
- Update test-requirement from pep8 to flake8

Change-Id: I4202f4e62f4e0412c62ef5b8b51492abf0717d4c
Signed-off-by: Thanh Ha <09ea4d3a79c8bee41a16519f6a431f6bc0fd8d6f@linuxfoundation.org>

opendaylight/spectrometer,opendaylight/spectrometer,opendaylight/spectrometer,opendaylight/spectrometer