tests: improve debug output

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>

spread.yaml

@@ -184,8 +184,14 @@ prepare-each: |
     dmesg -c > /dev/null
 
 debug-each: |
+    echo '# journal messages for snapd'
     journalctl -u snapd
+    echo '# apparmor denials '
     dmesg | grep DENIED || true
+    echo '# seccomp denials (kills) '
+    dmesg | grep 1326 || true
+    echo '# snap interfaces'
+    snap interfaces || true
 
 rename:
     # Move content into a directory, so that deltas computed by repack benefit