System tests - get working under podman-in-podman

Skopeo CI tests run under podman; hence the registries
run in the tests will be podman-in-podman. This requires
complex muckery to make work:

 - install bats, jq, and podman in the test image
 - add new test-system Make target. It runs podman
   with /var/lib/containers bind-mounted to a tmpdir
   and with other necessary options; and invokes a
   test script that hack-edits /etc/containers/storage.conf
   before running podman for the first time.
 - add --cgroup-manager=cgroupfs option to podman
   invocations in BATS: without this, podman-in-podman
   fails with:
       systemd cgroup flag passed, but systemd support for managing cgroups is not available

Also: gpg --pinentry-mode option is not available on all
our test platforms. Check for it before using.

Signed-off-by: Ed Santiago <santiago@redhat.com>

hack/make/test-system

@@ -0,0 +1,18 @@
+#!/bin/bash
+set -e
+
+# Before running podman for the first time, make sure
+# to set storage to vfs (not overlay): podman-in-podman
+# doesn't work with overlay. And, disable mountopt,
+# which causes error with vfs.
+sed -i \
+    -e 's/^driver\s*=.*/driver = "vfs"/' \
+    -e 's/^mountopt/#mountopt/' \
+    /etc/containers/storage.conf
+
+# Build skopeo, install into /usr/bin
+make binary-local ${BUILDTAGS:+BUILDTAGS="$BUILDTAGS"}
+make install
+
+# Run tests
+SKOPEO_BINARY=/usr/bin/skopeo bats --tap systemtest