reverts removal of parallel run from critest

Signed-off-by: Paul S. Schweigert <paulschw@us.ibm.com>

As discussed in https://github.com/containerd/containerd/issues/6903,
running ginkgo tests in parallel while trying to skip wasn't working.
However, now that
https://github.com/kubernetes-sigs/cri-tools/pull/930 has fixed the
issue upstream, we can revert back to running our tests in parallel
with the skip.

Vagrantfile

@@ -271,8 +271,7 @@ EOF
         fi
         trap cleanup EXIT
         ctr version
-        # TODO run in parallel, see https://github.com/containerd/containerd/issues/6903
-        critest --ginkgo.skip='HostIpc is true' --report-dir="${REPORT_DIR}"
+        critest --parallel=$[$(nproc)+2] --ginkgo.skip='HostIpc is true' --report-dir="${REPORT_DIR}"
     SHELL
   end