katello agent comparability with pulp 2.4.

Changes to the katello agent for compatibility with pulp 2.4 and gofer 1.0+.
- Pulp agent queue names format changed: pulp.agent.<id>.
- The @import directive no longer supported in plugin descriptors.  Functionality moved to code in the plugin.
- Use @initializer to explicitly initialize the plugin.  Replaces scheduled actions that only run once in 100 years.
- Some functionality implemented as classes but cleaner as plain old functions.
- Added 22 unit tests for 100% coverage.