waf: add a script that compares configurations

waf: add a script that compares configurations

This script is intended for use with the cross-build infrastructure
self-test during autobuild.

The script takes two or more "default.cache.py" files which are the
result of the waf configure process, and performs an intelligent
comparison - allowing for a limited set of variables to be different.

If the configurations are identical (apart from allowed differences) then
the script exit with 0 code.
If there are differences, the script outputs them to standard output
in unified diff format.

Signed-off-by: Uri Simchoni <urisimchoni@gmail.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>