Implement "env" command for internal ssh

[sapk]

Currently we ignore env passed via SSH. This even create some bug on windows without env local command.

We need to (re-)implement the part (that did nothing) disabled in #6825 via filling an array of env variable to be set to cmd.Env for later call of exec.

The tricky part of this implemntation is that we should filter and sanitize some variables and input passed to this command.

If you think of env variable that we should filter, please comment this issue.