Various issues in scripts

I've noticed that [shellcheck](https://www.shellcheck.net/) picks up numerous real issues with the scripts in this repo. For example this is a commit fixing only the issue of `local` not propagating the return value from assignment (which means the `$?` checks after it will never fail) https://github.com/viraptor/aws-codedeploy-samples/commit/9d55660264c544080bf6c3e90972db10e90ef21a
There are a few others as well.

It looks like the scripts could use a cleanup beyond a single PR.