fix(xcat-core): assert the integration case actually ran its tests

The case gated only on rc==0, but prove exits 0 both when tests pass and
when every test skips, so the case could report green having run nothing
at all. That is not hypothetical: all three tests carry environment
guards, and on the pull request run the harness discards a passing
case's output, so there was no way to tell from the log whether anything
had executed.

Add check:output=~Files=3, which proves prove found all three files. It
still tolerates a legitimate skip on a node without Kea, and it catches
a packaging regression or a rename. A missing directory was already
caught, since prove -r on a nonexistent path exits 2.

The count has to be maintained by hand when tests are added here, which
the README now says.

Signed-off-by: Daniel Hilst <392820+dhilst@users.noreply.github.com>
(cherry picked from commit 764e667e0a)

xCAT-test/autotest/testcase/integration/cases0

@@ -4,4 +4,5 @@ os:Linux
 label:mn_only,ci_test,integration
 cmd:prove -I/opt/xcat/lib/perl -I/opt/xcat/lib/perl/xCAT -r /opt/xcat/share/xcat/tools/autotest/integration
 check:rc==0
+check:output=~Files=3
 end

xCAT-test/integration/README.md

@@ -27,6 +27,14 @@ against it.
 Note the `-I` flags: unlike the unit tests these run from the installed location, so
 they pick up xCAT modules from `/opt/xcat/lib/perl` rather than from a source tree.
 
+The case checks `rc==0` and `output=~Files=3`. The second assertion is there because
+`prove` exits 0 both when tests pass and when they all skip, so `rc==0` alone would let
+the case report green having run nothing. Matching `Files=3` proves `prove` actually
+found all three files, which catches a packaging regression or a file being renamed
+without the count being updated here. **Add to that number when you add a test.** A
+missing directory is already caught by `rc==0` -- `prove -r` on a path that does not
+exist exits 2.
+
 Note also that `github_action_xcat_test.pl` invokes each case through `sudo`, so in CI
 these tests run as **root** while the unit tests run unprivileged. That is the right
 way round -- integration tests legitimately need to write to places like `/etc/kea`,