HTCondorLatentBuildslave args and docs; rename drmaa.py

Python-ified HTCondorLatentBuildSlave argument passing to allow users
to modify certain aspects of the job submission and specify arbitrary
items to add to the submit description via the extra_submit_description
keyword argument; and wrote much-improved docstrings.

Still need to update the htcondor.cfg sample, and add sample use cases
for different requirements such as having big-job and small-job slaves,
now that the resource requests can be varied for different buildslaves.

Renamed drmaa.py to drmaabot.py to avoid import name confusion with
Enrico Sirola's drmaa-python API.