Remove fail_with from check method

[bcoles]

Remove fail_with call from check method in exim4_deliver_message_priv_esc module as this was crashing the local exploit suggester module. Resolves #13850.

Also slightly improves the module logic. The module falsely believed that the only two session types are shell or meterpreter. This ignores ssh and is not future-proof. This PR modifies the logic to check for session.type != 'meterpreter' instead of session.type == 'shell'.

[adfoster-r7]

Release Notes

Removed fail_with() call from check method in the exim4_deliver_message_priv_esc module, as this was crashing the local exploit suggester module.