Throttle failing services, e.g., tty, on error exit code

Some 'respawn' type services, like gettys, may hog the CPU in error
states if the service immediately exits.  E.g., due to missing dev.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/ChangeLog.md

@@ -37,6 +37,9 @@ The Finit project now has a new home page: <https://finit-project.github.io>
 - Add memory field to `initctl --json` status output for cgroup-enabled
   services
 - Hide cursor at boot and shutdown for cleaner visual experience
+- Services with `respawn` option (including TTYs) now delay retry on non-zero
+  exit codes instead of immediate respawn.  Prevents busy-loop when service
+  fails repeatedly, which on some systems may have a crippling effect
 
 ### Fixes
 - Fix #453: RTC plugin fixes by Ming Liu, Atlas Copco