Update debconfmod.py

Within the debconfmod state module, when boolean debconf data is set, the resulting 'True' and 'False' values are invalid which should be 'true' / 'false'. Invalid datas are overridden when a dpkg-reconfigure <package> command is non-interactively executed, resulting in broken states.

For example, the 'exim4-config' package in Debian requires 'exim4/dc_minimaldns' key; which is a boolean. This key, and any other boolean keys will be unavailable for debconf state module, without this fix.