devenv: add `ssh-config-alias` option

This commit adds an option `--ssh-config-alias` to `build/devenv launch`
that allows specifying an alias that will be added or updated in
`$HOME/.ssh/config` to point to the devenv being launched. This is
essentially a custom `--ssh-config-verifier` option.
Merge pull request #146 from dobbymoodge/ssh_config_alias

Merged by openshift-bot