shell_cmd(): debug error handling

When the shell command had a returncode >0 the method check_output() would
raise an exception. This meant that the print() statement wasn't executed.

The changeset retreives the output of check_output() via an attribute of the
exception.

Signed-off-by: Erik Bernoth <erik.bernoth@gmail.com>
shell commands: elegant stderr handling

check_output() already provides a parameter to also grab all the stderr
created while it is executed. Using this parameter is more reasonable than
ending each shell command with manually redirecting the stderr.

Signed-off-by: Erik Bernoth <erik.bernoth@gmail.com>
specific test call: also print TAP results

Until now only autotest resulted in printed TAP format results. Thus the print
method was moved to test().

Signed-off-by: Erik Bernoth <erik.bernoth@gmail.com>
use constants when they exist: suite_pre

Signed-off-by: Erik Bernoth <erik.bernoth@gmail.com>
Release 0.2.1: debug TAP output

Signed-off-by: Erik Bernoth <erik.bernoth@gmail.com>