add chronic-like testsuccess/testfailure helpers

add chronic-like testsuccess/testfailure helpers

For many commands the output isn't stable (like then dpkg is called) but
the exitcode is, so this helper enhances the common && msgpass ||
msgfail by generating automatically a msgtest and showing the output of
the command in case of failure instead of discarding it unconditionally,
the later being chronic-like behaviour

Git-Dch: Ignore