Build failures should be less ugly

[rtyler]

Running the command in Vagrant with "execute": echo "This should fail the build!"
exit 1
This should fail the build!

ERROR: The following SSH command responded with a non-zero exit status.
Vagrant assumes that this means the command failed!

echo "This should fail the build!"
exit 1 (Vagrant::Errors::VagrantError)
/home/tyler/.rvm/gems/jruby-1.6.5.1@vagrant-plugin/gems/vagrant-1.0.0/lib/vagrant/communication/ssh.rb:62:in `execute'
org/jruby/RubyBasicObject.java:1694:in `__send__'
org/jruby/RubyKernel.java:2118:in `send'
/home/tyler/source/github/vagrant-plugin/models/vagrant_builder.rb:30:in `perform'
/home/tyler/.rvm/gems/jruby-1.6.5.1@vagrant-plugin/gems/jenkins-plugin-runtime-0.1.26/lib/jenkins/plugin/proxies/build_step.rb:14:in `perform'
/home/tyler/.rvm/gems/jruby-1.6.5.1@vagrant-plugin/gems/jenkins-plugin-runtime-0.1.26/lib/jenkins/plugin/proxies/build_step.rb:22:in `boolean_result'
/home/tyler/.rvm/gems/jruby-1.6.5.1@vagrant-plugin/gems/jenkins-plugin-runtime-0.1.26/lib/jenkins/plugin/proxies/build_step.rb:13:in `perform'

Build step 'Execute shell script in Vagrant' marked build as failure
Build finished, destroying the Vagrant box
Finished: FAILURE

SO UGLY