store/java: more -storepass values?

[adamdecaf]

On some installs changeit isn't the right value for -storepass. Should we offer an env variable in that event? Add some more common values? (i.e. password)

I don't want to make this a cli flag as installs with a non-standard value probably have a good reason for that.

We'll need to pass through whatever env value down to the os/exec calls of keytool.