Reference jenkins_common_home in config and git paths

playbooks/roles/jenkins_common/defaults/main.yml

 jenkins_common_user: jenkins
 jenkins_common_group: jenkins
 jenkins_common_home: /var/lib/jenkins
-jenkins_common_config_path: /var/lib/jenkins/init-configs
+jenkins_common_config_path: '{{ jenkins_common_home }}/init-configs'
 jenkins_common_port: 8080
 jenkins_common_version: jenkins_1.651.3
 jenkins_common_war_source: https://s3.amazonaws.com/edx-testeng-tools/jenkins
@@ -21,7 +21,7 @@ jenkins_common_debian_pkgs:
 jenkins_common_configuration_git_url: https://github.com/edx/jenkins-configuration.git
 jenkins_common_jenkins_configuration_branch: master
 jenkins_common_configuration_src_path: src/main/groovy
-jenkins_common_git_home: /var/lib/jenkins/git
+jenkins_common_git_home: '{{ jenkins_common_home }}/git'
 
 jenkins_common_configuration_scripts: []
 jenkins_common_non_plugin_template_files: