Fixed detection of latest gocd version under apt.

I found that this role no longer worked on debian systems since 089b658012bb3ca1abed5cac0544b30282d7ce65 (Ubuntu in my case) because it was trying to run the shell command `apt list go-server` and the command `apt` is not a valid one.

In this PR I've split it out into a yum-specific task and an apt-specific one (tweaked to get a correct latest version) following the way the rest of go-common.yml is done.