Provide a way to suppress load of unit tests

[isc-tleavitt]

https://github.com/intersystems/ipm/blob/main/src/cls/IPM/ResourceProcessor/Test.cls should have some switch to suppress load of unit tests.

e.g., if I want to just run:
zpm "mypackage test -only -DUnitTest.Case=UnitTest.mypackage.Something"

I shouldn't need to wait for all the unit tests to load.