Change buildtags based on installed environment.

Determine if selinux is available before building cri-o with support.
Don't add ostree support to crio or any tools other then kpod.
cri-o does not use ostree.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

hack/ostree_tag.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+if ! pkg-config ostree-1 2> /dev/null ; then
+	echo containers_image_ostree_stub
+fi

hack/selinux_tag.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+if pkg-config libselinux 2> /dev/null ; then
+	echo selinux
+fi