Added command for updating base image in multiple Dockerfiles

- Added command for updating base image in multiple Dockerfiles
- Merged the command which cleans yum metadata into install command
Wouldn't be better to chain all the yum commands into a single RUN, so that less intermediary images are used? 

Something like:

    RUN yum -y update && yum -y install java-1.7.0-openjdk-devel unzip && yum clean all