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
Commands in Dockerfile should be logically grouped. IMO, commands for updating and installing additional required packages should be separate. Every single line/command in Dockerfile will create a layer and it is useful to have them logically grouped because:
a. One can see the files changed (diff) in two different layers
b. A layer (command in Dockerfile) can be identified as identical and used as cache while building other images.