Remove unnecessary block on threads
Remove unnecessary block on threads

ServiceChecks are subclasses of Thread Class and are flagged as
“daemon thread” and we don't need to wait for them to finish for
exiting the main thread. Thus, we remove the unnecessary join(),
which blocks calling thread(the main thread in this case).
NOTE: These threads don't have any open file descriptors and don't
perform any kind of write IO operations, thus it is safe to let them
die when main thread exits. They use subprocess to fire-up the checks
but close_fds is set True, so they wont leak any file descriptors.

unixsurfer/anycast_healthchecker,unixsurfer/anycast_healthchecker,unixsurfer/anycast_healthchecker