Hooks - Better error handling and logging

[piotrmacha]

Current hook runner doesn't verify return code of scripts and treats every execution as succesful. When we use hooks to include additional steps in the build pipeline, it's confusing when an important script fails without any indication.

I propose 2 changes:

1. Log warn if hook exit code is not 0
2. Log hook standard output and standard error when verbosity is Detailed

Both features are verified by corresponding unit test.