haproxy_ctld_daemon.rb: Fix backtrace option

The haproxy_ctld_daemon.rb script in the haproxy cartridge had a typo:
':backgrace' instead of ':backtrace'.

This typo appears to have been present since haproxy_ctld_daemon.rb was
introduced in commit ee8cebbe1adb351a3b80ca3fda4f047aee8fac1b.
Card 57 - provide simple visual branding to the admin console
Card 57 - review feedback
Card 57 - update Gemfiles to use rubygems sass-twitter-bootstrap
Card 57 - make admin console header responsive
Card 57 - make admin console pages responsive
Adding Fedora vs RHEL cases for idler.
Ruby 2.0 in F19 runs as ruby-mri vs ruby in RHEL
<admin-console> broker proxy RPP change + filling in README
<admin-console> adding some configuration options
Card 57 - make histograms responsive
<admin-console> revising packaging
Automatic commit of package [openshift-origin-cartridge-jbossews] release [0.7.2-1].
Automatic commit of package [rubygem-openshift-origin-msg-broker-mcollective] release [1.12.2-1].
Automatic commit of package [openshift-origin-cartridge-10gen-mms-agent] release [1.26.2-1].
Automatic commit of package [rubygem-openshift-origin-node] release [1.12.2-1].
Automatic commit of package [openshift-origin-cartridge-nodejs] release [1.13.2-1].
Automatic commit of package [openshift-origin-cartridge-haproxy] release [0.7.2-1].
Automatic commit of package [openshift-origin-broker-util] release [1.12.2-1].
Automatic commit of package [rubygem-openshift-origin-common] release [1.12.2-1].
Automatic commit of package [openshift-origin-cartridge-postgresql] release [0.5.2-1].