check_dns: added test for nonresponsive dns server (#982)

Signed-off-by: Sven Nierlein <sven@nierlein.de>
travis-ci: create MySQL database 'test'
check_ping: output perfdata in seconds

This patch adds an option -s, --seconds to display perfdata in seconds rather than milliseconds. It is very useful for systems which scale the perfdata, i.e. Centreon.

Thanks to Oskar Liljeblad
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Closes #1025
Closes #1176