Add pytest-flask to test requirements
Add pytest-flask to test requirements

Change-Id: I7120f61f3d9a50f4b714fd14de1cf59aeab6eee0
Signed-off-by: Thanh Ha <09ea4d3a79c8bee41a16519f6a431f6bc0fd8d6f@linuxfoundation.org>

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