Jortel node unit coverage

This effort was to clean up the existing tests and add tests to address gaps in coverage.  Though not 100% across the board, the result of this work is pretty solid coverage.  The focus was on core functionality and budgeted to 24 hours.  The unit tests that will be included in cancellation will bump the coverage in a few modules.  A follow up effort to address *pulp_node.extensions* coverage would be a good idea.

```
Name                                      Stmts   Miss  Cover
-------------------------------------------------------------
pulp_node                                     2      0   100%
pulp_node.constants                          17      0   100%
pulp_node.distributors                        0      0   100%
pulp_node.distributors.http                   0      0   100%
pulp_node.distributors.http.distributor     102      5    95%
pulp_node.distributors.http.publisher        15      0   100%
pulp_node.distributors.publisher             47      1    98%
pulp_node.error                             107      0   100%
pulp_node.extension                          30     21    30%
pulp_node.extensions                          2      0   100%
pulp_node.extensions.admin                    0      0   100%
pulp_node.extensions.admin.commands         344    121    65%
pulp_node.extensions.admin.rendering         98     37    62%
pulp_node.extensions.consumer                 0      0   100%
pulp_node.extensions.consumer.commands      151     51    66%
pulp_node.handlers                            0      0   100%
pulp_node.handlers.handler                   39      1    97%
pulp_node.handlers.model                    248     33    87%
pulp_node.handlers.reports                   55      1    98%
pulp_node.handlers.strategies               110      3    97%
pulp_node.handlers.validation                50      3    94%
pulp_node.importers                           0      0   100%
pulp_node.importers.download                 34      1    97%
pulp_node.importers.http                      0      0   100%
pulp_node.importers.http.importer            58      3    95%
pulp_node.importers.inventory                26      1    96%
pulp_node.importers.reports                  15      1    93%
pulp_node.importers.strategies              134      5    96%
pulp_node.link                               40      0   100%
pulp_node.manifest                          120      1    99%
pulp_node.poller                             39      5    87%
pulp_node.reports                            55      0   100%
-------------------------------------------------------------
TOTAL                                      1938    294    85%
-------------------------------------------------------------
Ran 100 tests in 80.377s
```