jenkins: Add Jenkins Docker slave configuration files

Scripts and configuration files to set up Docker images which can be
used as dynamically-created Jenkins build workers through the Jenkins
Docker plugin.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #576 from euanh/jenkins

jenkins: Add Jenkins Docker slave configuration files
jenkins: Add CentOS 7 Dockerfile

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #577 from euanh/jenkins

jenkins: Add CentOS 7 Dockerfile
jenkins: Add wrapper scripts to run Docker containers

 * run-server.sh creates a container in detached mode, as used by Jenkins.
   For convenience it prints the new container's ID and the ssh command to
   log into it.

 * run-interactive.sh creates a container in interactive mode, running bash.
   The container will be destroyed when the shell exits.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #578 from euanh/jenkins

jenkins: Add wrapper scripts to run Docker containers