Add a check_install function

[tomMoral]

First of all, thanks a lot for this cool package!

I am developping a tool where I need to install programmatically julia and pyjulia in a conda env. This process is a bit complicated by the need to call julia.install() once pyjulia has been installed in python, as it seems that there is no tool to check if the installation has already been finished or not. In this context, it would be very useful to have a utility tool in pyjulia that check if the install is completed or not and that does not depend on the install completion. This could also allow for systematically calling julia.install() on import when the install has not been run before, removing one step to the install from the users (in which case such tool would just be a private functionality).

Do you think adding such function would be possible/interesting? Sorry if this has already been discussed, I could not find any reference to it.