kunit: Run all KUnit tests through allyesconfig

kunit: Run all KUnit tests through allyesconfig

Implemented the functionality to run all KUnit tests through kunit_tool
by specifying an --alltests flag, which builds UML with allyesconfig
enabled, and consequently runs every KUnit test. A new function was
added to kunit_kernel: make_allyesconfig.
Firstly, if --alltests is specified, kunit.py triggers build_um_kernel
which call make_allyesconfig. This function calls the make command,
disables the broken configs that would otherwise prevent UML from
building, then starts the kernel with all possible configurations
enabled. All stdout and stderr is sent to test.log and read from there
then fed through kunit_parser to parse the tests to the user. Also added
a signal_handler in case kunit is interrupted while running.
Tested: Run under different conditions such as testing with
--raw_output, testing program interrupt then immediately running kunit
again without --alltests and making sure to clean the console.

Signed-off-by: Heidi Fahim <heidifahim@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>