refs #2127 - instantiate exception and pass i18n arg correctly

<pre>
2.0.0-p353 :001 > PasswordCrypt.passw_crypt("a", "b")
NoMethodError: undefined method `Exception' for Foreman:Module
	from /home/dcleal/code/foreman/foreman/app/services/password_crypt.rb:5:in `passw_crypt'
</pre>

<pre>
2.0.0-p353 :001 > PasswordCrypt.passw_crypt("a", "b")
Foreman::Exception: ERF42-5628 [Foreman::Exception]: »Unsupported password hash function 'b'«
	from /home/dcleal/code/foreman/foreman/app/services/password_crypt.rb:5:in `passw_crypt'
</pre>