Refactored PollingCommand and added unit tests. This commit does not
change existing uses of PollingCommand, so they are broken until my next
commit.
Actual refactoring from the last commit, the previous one was just the
new empty files
Refactoring of the commands that use PollingCommand for its new APIs
Added pulp_devel package and moved task simulator to it, fixing
platform units as necessary
Added devel tests to run-tests.py
Merge pull request #379 from pulp/jdob-async-base-commands

PollingCommand refactoring and pulp_devel package