Update check_rabbitmq_watermark like PR#12 & PR#9

Apply jamesc/nagios-plugins-rabbitmq#12 jamesc/nagios-plugins-rabbitmq#9 to
check_rabbitmq_watermark.
Merge remote-tracking branch 'simmel/fixup_watermark'
Small documentation changes
Small documentation update
Added documentation for the node argument
Added documentation for the node argument
Merge pull request #15 from elmer-garduno/master

Thanks for the commit !
removed conflicting argument

--port doesn't have a short argument in the others files, so removed from here.
Add --(no-)?-proxy option to all scripts to allow bypassing the environment http proxy
Merge branch 'dev/noenvproxy'
Merge remote-tracking branch 'pmoranga/patch-1'