Return correct exit code upon signal + SIGQUIT now quits without cleanup

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Allow force sigint and allow sigquit after sigint

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Merge pull request #4980 from creack/update_signal_management

Return correct exit code upon signal + SIGQUIT now quits without cleanup