Fix generation of sample policy files

Generation of sample policy files was broken when exclude_deprecated was
added as an extra argument to the generate_sample function in
I6d02eb4d8f94323a806fab991ba2f1c3bbf71d04. It was passed as the fourth
argument, which is actually include_help. Because it defaults to False,
this turned sample policy files into actual policy files.

Fix by using keyword arguments instead.

Change-Id: I5478b1c8e7fd2f1b01f63602998194bab3683f7c
Closes-Bug: #1975682