Fix event handlers on ruby 2

Fixes #4219.

Because `#respond_to?` no longer returns true for protected methods, the block that actually calls all the event subscribers was dead code on Ruby 2.x

### Verification
 - [x] Make sure you're using Ruby 2.1.x
 - [x] Get a session
 - [x] **Verify** Output contains:
```
[*] Command shell session 1 opened
```