Comment 12 for bug 1272083

Again, thanks for taking time to review HPCC Charm. Based on the 3rd review we made following changes:
1) Add restart in start hook

2) Add checksum validation. We add a string package-checksum in config.yaml. If it is not empty install script will use it to validate the downloaded package before install. In future our download site will provide md5sum file so validate will be conducted automatically wihtout this setting.

3) Fix the open-port which was broken before.

4) Add implementation to automatically generate ssh key pair if user doesn't provide them in config.yaml. Basically if no keys supplied in config.yaml every new joined node will try to use existing ssh keys through relation-get. If can find it will call ssh-keygen to create new pair. In relation-chanage hook every node will use the keys from lowest ip node if there are different thant its pair. It shouldn't have overhead since when every nodes has the same pair of key. We tested in various scenarios, for example deploy multiple nodes, add new nodes, etc. There is a restriction: user can not change the keys setting in config.yaml after the charm deployed. It will be added in future enhancement.

5) We add CentOS prerequisite but never test it. Actually we are not sure if current juju charm support CentOS or Fedora.