TECH-1204 - Adding the health-check functionality to Chief-Keeper

[OleksandrUA]

1. Chief-Keeper starts as a loop processing blocks calling process_block() method
2. With this PR we add @healthy decorator which once called writes current UNIX timestamp to /tmp/health.log
3. We also add health-check.sh script which compares current UNIX timestamp with one in file /tmp/health.log
4. If delta is more than 15 minutes exit code = 1, if less -- 0
5. We will execute health-check.sh as ECS task health-check

[jeannettemcd]

Does the file need to be closed after writing to it ? We don't what to have a leak, or exceed the ulimit.

[OleksandrUA]

@jeannettemcd thanks, when with is used Python creates a temporary context space and once Python exits from the with block/context, the file is automatically closed