config: noise reduction + doc update

*  Excessive complaining on every test if
   unknown, non-ini file found in a config dir.

*  Updated config_custom README file.

Signed-off-by: Chris Evich <cevich@redhat.com>
subtests...start: long_term_app unused import

Signed-off-by: Chris Evich <cevich@redhat.com>
run_pylint: Allow checking specific files

Signed-off-by: Chris Evich <cevich@redhat.com>
dockertest.containers: Add attribute for remove method

Signed-off-by: Chris Evich <cevich@redhat.com>
subtests...rm: Improve logging & reliability

Signed-off-by: Chris Evich <cevich@redhat.com>
subtests...psa: Improve logging & reliability

Signed-off-by: Chris Evich <cevich@redhat.com>
subtests...inspect: Minor config. cleanup

Signed-off-by: Chris Evich <cevich@redhat.com>