We need to be able to exclude dependencies from the python module
dependency code. Add support for the vardepexclude flag for these. It
only works from the configuration namespace rather than per recipe
for efficiency.
(Bitbake rev: 1aa672b01037fda4ca82f2c7e394783287c09ecd)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>