Make gate-solum-requirements non-voting

In solum we are using python-solumclient as a dependent package. But
python-solumclient cannot be added to global requirements as it is not
part of OpenStack. For now just make the requirements gate non-voting.

Change-Id: I1df12684a552fa11d9a05d2e6da0c46742564cca
Merge "Make gate-solum-requirements non-voting"