Fix build configuration to properly build test_libpluto and unit_tests

[bondhugula]

Fix build configuration to properly build test_libpluto and unit_tests. unit_tests isn't cleaned on a make clean and both binaries aren't built the proper way via automake but via custom patch work to the top level Makefile.am.

A make at the top level doesn't build test_libpluto and make test_libpluto before doing a make to build pluto would fail. make pluto test_libpluto would also fail since the latter's dependency isn't properly setup.

This in turn forces the github CI to first run make followed by make test_libpluto and make unit_tests.