How to change the default command to open shells in the MobileTerminal Cydia package
This is a function of the shell set for the user in /etc/passwd (/etc/master.passwd).  Normally you can change this via the chsh command, but iOS7 doesn't have this command. so you need to edit /etc/passwd and /etc/master.passwd (as root) and change the shell for the user mobile to /bin/bash.

So it should look like:

mobile:*:501:501:Mobile User:/var/mobile:/bin/bash


after changing from:

mobile:*:501:501:Mobile User:/var/mobile:/bin/sh


Note: in the master.passwd file the '*' will be your encrypted password.