Ensure privacyidea-pip-update compatibility with pip 9 and 10
Ensure privacyidea-pip-update compatibility with pip 9 and 10

Closes #1128

privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea