scheduler service throws error during shutdown if it wasn't initialized properly

There is some logic in the stop function of the scheduler service that assumes that "pool" and "jobs" have been initialized in the context. If they haven't, it will throw an NPE.

We saw this in an acceptance test failure, where a SIGINT was sent to the server while it was still initializing the app, and this caused the shutdown sequence to start.

http://jenkins-enterprise.delivery.puppetlabs.net/view/pe-puppet-server-extensions/job/enterprise_pe-puppet-server-extensions_integration-system_smoke-master/10/LAYOUT=64mdca,LDAP_TYPE=default,PLATFORM=centos7,label=beaker/consoleFull