BAD-38: Override clean-all target for HDP 1.2 shim

clean-all targets normally wipe out the lib folder of the project, as the lib folder is normally filled by Ivy resolve tasks.  In the case of the HDP 1.2 shim, the JARs are not available to Ivy and thus we had to check them in, and we don't want to wipe out the lib folder in this case. So I just overrode the clean-all target to call clean instead.