Fix incorrect test.

The packaging.install.remove function (a.k.a. the uninstall feature)
takes a path argument to allow client code to use custom directories
instead of sys.path.  The test used to give self.root_dir as path, which
corresponds to a prefix option, but prefix is not on sys.path, it’s only
the base directory used to compute the stdlib and site-packages
directory paths.  The test now gives a valid site-packages path to the
function.

Lib/packaging/tests/test_uninstall.py

@@ -89,9 +89,10 @@ class UninstallTestCase(support.TempdirManager,
         site_packages = self.get_path(dist, 'purelib')
         return dist, site_packages
 
-    def test_uninstall_unknow_distribution(self):
+    def test_uninstall_unknown_distribution(self):
+        dist, site_packages = self.install_dist('Foospam')
         self.assertRaises(PackagingError, remove, 'Foo',
-                          paths=[self.root_dir])
+                          paths=[site_packages])
 
     def test_uninstall(self):
         dist, site_packages = self.install_dist()