busybox/gtk/perl/base-passwd: Ensure data is correctly expanded

busybox/gtk/perl/base-passwd: Ensure data is correctly expanded

Where variables are used in python, we need to ensure they are expanded.
This happens to work at the moment but likely will not happen in future
and isn't good code practise.

Its mostly an issue around key values, since bitbake has already
performed key expansion when these functions are executed.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>