Add get() to htcondor.param if missing

Old versions of condor-python do not have htcondor.param.get(); monkey-patch
htcondor.param if that is the case. This makes the code less repetitive than
using try/except blocks.

Also, "'foo' in htcondor.param" doesn't work in old versions of condor-python
so replace uses of that with htcondor.param.get()

This is a replacement for the pull request in #31.
At this place - and in the condor_ce_config_generator script - you also need to add this attribute to COLLECTOR_ATTRS.  Otherwise, the config parameter won't be included in the collector ClassAd.

Did you get a chance to test this?