Added hostlist argument

option to define a comma separated host list as an argument
Handling cases where herd.py is symlinked to another location

For instance, when in /usr/bin as per proper package install.
Merge branch 'master' of github.com:dominis/Herd

* 'master' of github.com:dominis/Herd:
  Revert "nice+ionice test"
  nice+ionice test
  Handling cases where herd.py is symlinked to another location
  Added hostlist argument