Make "clone-build-slave" job more resilient to DNS failures

[prakashsurya]

There's been a failure in the clone-build-slave job where dcenter.delphix.com failed to resolve: http://build.prakashsurya.com:8080/job/clone-build-slave/39/console

PLAY [dcenter.delphix.com] **************************************************** 

GATHERING FACTS *************************************************************** 
<dcenter.delphix.com> ESTABLISH CONNECTION FOR USER: blackbox
<dcenter.delphix.com> REMOTE_MODULE setup
<dcenter.delphix.com> EXEC sshpass -d4 ssh -C -tt -vvv -o ControlMaster=auto -o ControlPersist=60s -o ControlPath="/var/lib/jenkins/.ansible/cp/ansible-ssh-%h-%p-%r" -o StrictHostKeyChecking=no -o GSSAPIAuthentication=no -o PubkeyAuthentication=no -o User=blackbox -o ConnectTimeout=10 dcenter.delphix.com /bin/sh -c 'mkdir -p /tmp/ansible-tmp-1446188076.55-78171385027248 && chmod a+rx /tmp/ansible-tmp-1446188076.55-78171385027248 && echo /tmp/ansible-tmp-1446188076.55-78171385027248'
fatal: [dcenter.delphix.com] => SSH Error: ssh: Could not resolve hostname dcenter.delphix.com: No address associated with hostname
It is sometimes useful to re-run the command using -vvvv, which prints SSH debug output to help diagnose the issue.

TASK: [snapshot-dc-instance | Check for snapshot_name variable] *************** 
FATAL: no hosts matched or all hosts have already failed -- aborting

In order to mitigate this issue, the IP for dcenter.delphix.com should be added to the /etc/hosts on the Jenkins master.