missing RPM dependency for big_catalogs

[rptaylor]

After installing python-cvmfsutils-0.4.1-2.10.obs.el7.noarch on CentOS 7.4 via yum from the contrib repo:

$ big_catalogs --help
Traceback (most recent call last):
  File "/usr/bin/big_catalogs", line 4, in <module>
    import cvmfs
  File "/usr/lib/python2.7/site-packages/cvmfs/__init__.py", line 10, in <module>
    from whitelist    import *
  File "/usr/lib/python2.7/site-packages/cvmfs/whitelist.py", line 10, in <module>
    from M2Crypto import RSA
ImportError: No module named M2Crypto

After installing m2crypto it worked, but the RPM should include this dependency.