Clean up lots of modules

A lot of module methods are optional, so let's remove them from the library modules if they're not used.
Should probably look at updating docs/shutit_module_template.py to make it clear what can be removed if it's not needed.
Additionally, it adds a shutit.run_script. Look at the casperjs module.
Additionally it cleans up the mysql module to use two new features, set_default_expect and set_default_child.
set_default_child is done in setup so it probably doesn't need to be changed. set_default_expect defaults to base_prompt. Note how it can be called, and thereafter (but only in that module method call, courtesy of metaclass magic) you can omit the expect argument.
Combining this with the shuitit.run_script call, it allows you to simplify modules massively and make it so you don't need a very wide screen to ready modules.