killprocs: add kill_delay setting

This allows containers using OpenRC based services to be configured to
allow open tcp connections to be closed before they are shut down.

This fixes #476.

conf.d/killprocs

@@ -4,3 +4,8 @@
 # The setting is called killall5_opts because the options here are meant
 # to be identical to those you could pass to killall5.
 killall5_opts=""
+
+# If you need to delay after each kill attempt during shutdown, set the amount
+# of time you need to delay here. This gets passed directly to sleep in
+# the shell.
+# kill_delay=0