support <processorpath> parameter in testCompile Mojo

[jan-feindt]

in TestCompileMojo getProcessorpathDependencies() returns null

please add support like in CompileMojo

[ifedorenko]

Do you mind giving some details about your usecase, i.e. why do you need test-specific processorpath?

[cyberwasp]

If we use processorpath in plugin than test's compile fails because annotationProcessors is in AbstractCompileMojo but getProcessorpathDependencies is in TestCompileMojo and return null