Module Plugins

Load modeling and monitoring plugins from standard locations and from
ZenPacks.  Most of the entry into this module is via the three functions
defined at the very bottom of the file. Those functions use the singleton
PluginManager objects to load the plugins.

Classes -
    PluginImportError - an exception type
    PluginLoader - jellyable object that has all the information neccessary
                   to dynamically import the plugin module and instantiate the
                   class that shares the module's name
    CoreImporter - jellyable object that is injected into a PluginLoader.
                   handles importing of plugins found inside Products
    PackImporter - same as above but for zenpack plugins
    BaseLoaderFactory - base class for the two loader factories
    CoreLoaderFactory - generates the PluginLoaders for core plugins
    PackLoaderFactory - generates the PluginLoaders for zenpack plugins
    PluginManager - there is one singleton instance of this class for modeling
                    plugins and another for monitoring plugins
                    
Note that modPath uses a different convention for core versus zenpack plugins.

    core: zenoss.cmd.uname
    zenpack: ZenPacks.zenoss.AixMonitor.modeler.plugins.zenoss.cmd.uname