client: add pyyaml to python client requirements.txt
client: add pyyaml to python client requirements.txt

opencb/opencga,opencb/opencga,j-coll/opencga,j-coll/opencga,j-coll/opencga,j-coll/opencga,j-coll/opencga,opencb/opencga,opencb/opencga,opencb/opencga,opencb/opencga,j-coll/opencga