Add test deptype (#5132)

* Add '--test=all' and '--test=root' options to test either the root or the root and all dependencies.
* add a test dependency type that is only used when --test is enabled.
* test dependencies are not added to the spec, but they are provided in the test environment.

var/spack/repos/builtin/packages/libpsl/package.py

@@ -39,8 +39,7 @@ class Libpsl(AutotoolsPackage):
     depends_on('pkg-config@0.9.0:', type='build')
     depends_on('python@2.7:', type='build')
 
-    # TODO: Add a 'test' deptype
-    # depends_on('valgrind', type='test')
+    depends_on('valgrind~mpi~boost', type='test')
 
     def configure_args(self):
         spec = self.spec