Added sanity check: is 'pillar' in self.opts

[redmcg]

This fixes an exception that is thrown when using the 'when' clause in a
master scheduler. The master does not appear to create a 'pillar' entry
in self.opts (hence you get an exception when trying to check if 'whens' is in self.opts['pillar']).

For example - the following schedule entry in the master config would create this exception:

schedule:
  test_master_schedule:
    function: myrunner.test
    when: 10:00pm