gather: nodeps should take packages from comps groups

When gather_method is set to nodeps, we should not ignore the comps
group that the method received. Instead it should find out which
packages are in those groups and take them into the compose.

In order for this to be of any reasonable use, the comps file needs to
include all dependencies for the packages.

Fixes: #653
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

tests/test_comps_wrapper.py

@@ -41,6 +41,17 @@ class CompsWrapperTest(unittest.TestCase):
             comps.get_comps_groups(),
             ['core', 'standard', 'text-internet', 'firefox', 'resilient-storage', 'basic-desktop'])
 
+    def test_get_packages(self):
+        comps = CompsWrapper(COMPS_FILE)
+        self.assertItemsEqual(
+            comps.get_packages('text-internet'),
+            {'dummy-elinks', 'dummy-tftp'})
+
+    def test_get_packages_for_non_existing_group(self):
+        comps = CompsWrapper(COMPS_FILE)
+        with self.assertRaises(KeyError):
+            comps.get_packages('foo')
+
     def test_write_comps(self):
         comps = CompsWrapper(COMPS_FILE)
         comps.write_comps(target_file=self.file.name)