test: Add identify client test
test: Add test for add_pollfd
test: Add test for deleting pollfds
test: Correct uid for client
core: Add signal handler to cleanup on INT and TERM
shared: Add workaround for client notification support

Because client's won't be notified synchronously but we'll need more
work in libbuxton to support client's polling for notifications, add
temporary support for notification messages through
buxton_wire_get_response.
test: Remove fork calls from check daemon

In order to improve consistency and tracking issues avoid forking
in check programs.