Fixed the Jenkins framework to reject master URLs with "http://".

Review: https://reviews.apache.org/r/12780
Removed the ability to manually provision Jenkins slaves.

Review: https://reviews.apache.org/r/12846
Fixed Slave, Cloud and Retention strategy for Jenkins.

Review: https://reviews.apache.org/r/12847
Fixed JenkinsScheduler to not crash when the Mesos
native library is not bundled with the plugin.

Review: https://reviews.apache.org/r/12884
Refactored Jenkins to make resources configurable.

Review: https://reviews.apache.org/r/12890