Upgrade java to 8 for jenkins

For some reason, Java has an arbitrary limit of 2048 bits DH keys, while id.fp.o accepts only 4096.
Java 8 supports ECDHE, so let's use that instead.

playbooks/groups/jenkins-cloud.yml

@@ -45,7 +45,7 @@
     - vim
     - dejavu-s\*
     - fontconfig
-    - java-1.6.0-openjdk
+    - java-1.8.0-openjdk
     - httpd
     - openssh-clients
     - git
@@ -310,8 +310,8 @@
     action: yum state=installed pkg={{ item }}
     with_items:
     - vim
-    - java-1.7.0-openjdk
-    - java-1.7.0-openjdk-devel
+    - java-1.8.0-openjdk
+    - java-1.8.0-openjdk-devel
     - subversion
     - bzr
     - git