logger: guarantee to flush the logs on exit
logger: guarantee to flush the logs on exit

Previously the logging was async, so there could be logs in the
buffer when the program quits (especially if it fails unexpectedly)

Signed-off-by: David Scott <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@recoil.org>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit