tests,ci: Move "test-basic" (bare mode) to installed test

Our CI uses default Docker, which has SELinux labeling but is rather
evil in returning `EOPNOTSUPP` to any attempts to set `security.selinux`,
even if to the same value.

The previous fire 🔥 for this was: https://github.com/ostreedev/ostree/pull/759

The `bare` repo mode really only makes sense as uid 0, so our installed
test framework is a good match for this.  However, the unit tests *do*
work in a privileged container even as non-root, and *also* should
work on SELinux-disabled systems.  So let's teach the test framework
how to skip in those situations.

I tested this both in a priv container (my default builder) and an unpriv
container (like our CI).

At the same time, start executing the `test-basic.sh` from an installed test,
so we get better coverage than before.

This is just the start - all of the sysroot tests really need the
same treatment.

Closes: #1217
Approved by: jlebon

tests/installed/fah-prep.sh

@@ -6,3 +6,5 @@ if lvm lvs atomicos/docker-pool &>/dev/null; then
     lvm lvremove -f atomicos/docker-pool
 fi
 lvm lvextend -r -l +100%FREE atomicos/root
+ostree admin unlock
+rsync -rlv ./ostree/insttree/usr/ /usr/

tests/installed/itest-bare-unit.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Run test-basic.sh as root.
+# https://github.com/ostreedev/ostree/pull/1199
+
+set -xeuo pipefail
+
+dn=$(dirname $0)
+. ${dn}/libinsttest.sh
+
+# Use /var/tmp to hopefully use XFS + O_TMPFILE etc.
+tempdir=$(mktemp -d /var/tmp/tap-test.XXXXXX)
+touch ${tempdir}/.testtmp
+function cleanup () {
+    if test -f ${tempdir}/.testtmp; then
+	      rm "${tempdir}" -rf
+    fi
+}
+trap cleanup EXIT
+cd ${tempdir}
+# This sort of bypasses the installed-tests spec;
+# fixing that would require installing g-d-t-r, though
+# more ideally we architect things with a "control" container
+# distinct from the host.
+/usr/libexec/installed-tests/libostree/test-basic.sh