Use python-krbV in EPEL
rpkg is moving to Python 3 compatiblity and now is using python-gssapi to
detect whether there is valid tickets in credential ccache. However,
python-gssapi is still not available in EPEL for RHEL. So, packages for RHEL
has to use old python-krbV for a while.
Request of making python-gssapi available in EPEL is created. Once it's done,
this change can be reverted.