This updates the script used to register the elasticsearch
snapshot repositories. It will first gather a list of all
currently registered repositories, then check for the existence
of each configured repository. If the repository exists, the job
will not attempt to register the repository again. If it doesn't
exist, the job will then register the desired repository
Change-Id: I2cfd3c44f1b2b4a54c9b07be79c2c87af77c540e