FIX: add way of completely skipping test that bugged with jessie

Tests are stored in a bash indexed array.
Bash on debian8 does not support arrays declaration and if there was no
registered tests, the array variable was seen as undefined.
With this way of completely dismissing the test suite, the problem is
fixed

tests/lib.sh

@@ -66,6 +66,10 @@ contain()
     fi
 }
 
+dismiss_test() {
+    dismiss_test=1
+}
+
 # test is expected to fail (for instance on blank system)
 # then the test wont be taken into account for test suite success
 dismiss_count_for_test() {