Pin to boto3 < 1.8
Pin to boto3 < 1.8

Boto3 1.8 breaks our tests using moto.  See
https://github.com/spulec/moto/issues/1793 .  We can unpin when moto is
updated.

This also has to add boto-core as a requirement to allow moto to
install.

Kitware/girder,girder/girder,jbeezley/girder,kotfic/girder,girder/girder,jbeezley/girder,Kitware/girder,data-exp-lab/girder,manthey/girder,data-exp-lab/girder,RafaelPalomar/girder,jbeezley/girder,jbeezley/girder,kotfic/girder,RafaelPalomar/girder,manthey/girder,RafaelPalomar/girder,Kitware/girder,RafaelPalomar/girder,kotfic/girder,RafaelPalomar/girder,Kitware/girder,manthey/girder,kotfic/girder,kotfic/girder,data-exp-lab/girder,data-exp-lab/girder,girder/girder,data-exp-lab/girder,girder/girder,manthey/girder