CentOS7: Can't build rpms without python-oauthlib

python-oathlib is not a strict dependency of the cloud-init package, but url_helper imports it without handling ImportErrors. This causes breaks on CentOS 7 when trying to build an RPM in an environment which doesn't have oauthlib.

make rpm
python3 ./packages/brpm --distro=redhat
Traceback (most recent call last):
  File "./packages/brpm", line 27, in <module>
    from cloudinit import templater
  File "/root/cloud-init/cloudinit/templater.py", line 31, in <module>
    from cloudinit import util
  File "/root/cloud-init/cloudinit/util.py", line 48, in <module>
    from cloudinit import url_helper
  File "/root/cloud-init/cloudinit/url_helper.py", line 20, in <module>
    import oauthlib.oauth1 as oauth1
ImportError: No module named 'oauthlib'
make: *** [rpm] Error 1