Add option for sending test results to mailing list only

... and clarify descriptions of the other options.

Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
3 jobs for master in 4 minutes and 32 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Containers
passed #113452
containers:patchwork-testing

00:02:53

 
  Test
failed #113492
test

00:01:38

failed #113453
test

00:01:23

 
Name Stage Failure
failed
test Test
pep8 installdeps: flake8
pep8 installed: entrypoints==0.3,flake8==3.7.5,mccabe==0.6.1,pycodestyle==2.5.0,pyflakes==2.1.0
pep8 run-test-pre: PYTHONHASHSEED='97883479'
pep8 runtests: commands[0] | flake8 patchwork patchwork/bin/pwclient git-pw/git-pw
___________________________________ summary ____________________________________
ERROR: py27-django111: commands failed
ERROR: py36-django111: commands failed
pep8: commands succeeded
ERROR: Job failed: exit code 1