Address issue where mount would fail when password had special characters

Hey Shea,
Got another small PR for you.  

We were getting a number of reports where the AFP mount was failing, and we tracked it down.  The problem was many of the passwords had special characters in them (and specifically @ signs), which would cause the mount -t afp .... call to fail.   

https://github.com/lindegroup/autopkgr/issues/177
https://github.com/lindegroup/autopkgr/issues/176

This should address that issue by using ```urllib.quote()``` to percent encode the password.  

I've tested with AFP, but not SMB (i don't have access to an smb server).
Also I haven't tested on an actual JSS since I don't manage any, but in concept it should work fine.

--Eldon