CI/CD: Install deps from ./requirements.txt before running unit tests
    
    Generally new dependencies added to waiverdb.spec are not installed
    to C3I Jenkins slave pod because of the limitation of OpenShift that no root access to pod.
    To apply the new set of dependencies, we have to rebuild the Jenkins slave pod image after
    the new waiverdb.spec is merged to master.
    
    This PR tries to mitigate this issue by installing additional PyPI dependencies to user directory
    `pip3 install --user -r ./requirements.txt`. This shouldn't have side effect because it doesn't update
    RPM installed packages unless `-U` is specified.