vmTools.commonDebPackages: Add "mawk".

While debugging an issue with running NixOps tests, I found out that the
output from debClosureGenerator is not deterministic.

The reason behind this is the way how Provides and Replaces fields are
handled. I haven't yet found out what's the exact issue, but so far
packages "Provides" are more or less picked at random.

So, running the NixOps Hetzner tests we get either mawk, original-awk or
gawk altering on every invocation.

While for the test it isn't poisionous whether wi have mawk or gawk,
having original-awk certainly is, because live-build only works with
mawk or gawk.

The best solution would obviously be to make debClosureGenerator
deterministic, but in the case of "Provides: awk", we can safely pick
mawk by default, because the latter has a "Priority: required" in its
package description.

This also has the advantage that we can safely cherry-pick this to
release-15.09 because it's very unlikely that we'll break the
debClosureGenerator by adding a dependency to commonDebPackages.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/build-support/vm/default.nix

@@ -1837,6 +1837,7 @@ rec {
     "bzip2"
     "tar"
     "grep"
+    "mawk"
     "sed"
     "findutils"
     "g++"