tests/containers-imperative: Include stdenvNoCC

While building the container there are a few occasions where stdenvNoCC
is used underneath. During the last staging merge, some change now tries
to build texinfo during the test while building stdenvNoCC.

With this change, I'm adding stdenvNoCC to the closure to make sure that
even when we have future stdenv changes, it doesn't break (well, except
if we do have another variation like stdenvNoCC that overrides stdenv).

I haven't bisected the exact change, but I'd suspect that it could be
one of the commits in #39457.

This fixes the test and it no longer fails with the following error:

error: unable to download 'http://ftpmirror.gnu.org/texinfo/texinfo-6.5.tar.xz

': Couldn't resolve host name (6)
builder for '/nix/store/r7sf1wjbnimwgnv276jh59nfnzw40x30-texinfo-6.5.tar.xz.drv' failed with exit code 1
cannot build derivation '/nix/store/5w1pv788ayi1wahyy76i90yqv96ai4h5-texinfo-6.5.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/cnsfkf0j5xmm14zzm5a3a66pz66gbc82-stdenv-linux.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/11kkhk57ic8kfd7g197sqwgd0pzqfjhl-nixos-system-foo-0-18.09pre-git.drv': 1 dependencies couldn't be built
error: build of '/nix/store/11kkhk57ic8kfd7g197sqwgd0pzqfjhl-nixos-system-foo-0-18.09pre-git.drv' failed
/run/current-system/sw/bin/nixos-container: failed to build initial container configuration

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @aristidb, @edolstra, @chaoflow, @kampfschlaefer