Write package whitelist for each variant

If we have a package set for the variant (which happens if there are
modules), include a list of all NEVRAs in the pungi kickstart.

This can be used to make sure only packages from correct tag get into
the compose. If two packages with same name but different version get
into the compose, this can help get even older version into a particular
variant.

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

tests/helpers.py

@@ -38,6 +38,7 @@ class MockVariant(mock.Mock):
         self.mmds = []
         self.arch_mmds = {}
         self.variants = {}
+        self.pkgset = mock.Mock(rpms_by_arch={})
 
     def __str__(self):
         return self.uid