Merge pull request #4557 from edx/youngstrom/bump-jenkins-heap-size

Bump jenkins heap size to 16 gb

playbooks/roles/jenkins_build/defaults/main.yml

 build_jenkins_user_uid: 1002
 build_jenkins_group_gid: 1004
 build_jenkins_version: jenkins_2.89.4
-build_jenkins_jvm_args: '-Djava.awt.headless=true -Xmx8192m'
+build_jenkins_jvm_args: '-Djava.awt.headless=true -Xmx16384m'
 build_jenkins_configuration_scripts:
   - 1addJarsToClasspath.groovy
   - 2checkInstalledPlugins.groovy