Fix module loading

Update to 2.8.1:

Feature improvements:

• Signature added for: sles 12sp2
• Signature added for: fedora 26
• Signature added for: ubuntu 17.04
• Signature added for: freebsd 10.3
• Signature added for: freebsd 11.0
• Signature added for: xen server 7.0
• Signature added for: xen server 7.1

Bugfixes:

• Cleanup distro_signatures
• Use $bind_master in secondary.template (#1720)
• Add zonename to metadata in manage_bind (#1700)
• Update cobbler.wsgi to Django >=1.4 API
• Add some input validation to repo configuration (#1741)
• Fix handling of multiple bridge interfaces (#1735)
• Added warnings in kickstart samples (#1737)
• Fix the auto-build when using autodiscovery (#1753)
• Fixes to setup.py so that python setup.py install now works again on Debian/Ubuntu (#1750)
• Replication now works with Cobbler using non standard ports (#1637)
• Generalize names for named/dhcpd executables in cobbler check (#1672)
• No more manual symlinks required for Python dist-packages on Debian/Ubuntu (#1751)
• Code cleanup in kickgen.py, setup.py, etc
• Fixes to several API calls relating to mgmtclass, file and package
• RHEL7 still needs to use the nameserver option
• Master interface now inherits MTU setting from slave interface
• Don't add multiple (bond) slave interfaces to dhcpd.conf
• Grub legacy loaders updated to the latest versions available
• Enable the source tree to be cloned on Windows systems (#1722)
• Minor SuSE AutoYast improvements