kunit: tool: fix improper treatment of file location

Commit 01397e82 ("kunit: Fix TabError, remove defconfig code and
handle when there is no kunitconfig") and commit 45ba7a89 ("kunit:
kunit_tool: Separate out config/build/exec/parse") introduced two
closely related issues which built off of each other: they excessively
created the build directory when not present and modified a constant
(constants in Python only exist by convention).

Together these issues broken a number of unit tests for KUnit tool, so
fix them.

Fixed up commit log to fic checkpatch commit description style error.
Shuah Khan <skhan@linuxfoundation.org>

Fixes: 01397e82 ("kunit: Fix TabError, remove defconfig code and handle when there is no kunitconfig")
Fixes: 45ba7a89 ("kunit: kunit_tool: Separate out config/build/exec/parse")
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>