#1 Plugin interface for RM adapter factory

[Chris Smith]

Currently, the different types of RM adapter (LSF and GRAM) are
hard-coded within the RM adapter factory code. This means that
every new RM adapter needs to be distinguished in this code.

What would be better is to have configuration which associates a
type of RM adapter with a class name which will provide the
implementation. This is similar to the scheduler plugin interface
and configuration.

The resourcemanager_config.xml file should support a new
element within the cluster element which indicates the class to use
for a given cluster.

Alternatively (perhaps better) is to have a separate set of
elements within the resourcemanager_config.xml file which
associates type names to classes. These defined types could then
be used within the cluster elements.