Greenplum: cancel backup on Postgres process failure

[usernamedt]

I propose to introduce the functionality to automatically cancel the backup if one of the following events occurs:

• WAL-G segment process failure
• Postgresql segment process failure

Also, I propose to introduce the following setting to control how frequently WAL-G will try to check if the Postgresql segment process is alive:

• WALG_ALIVE_CHECK_INTERVAL

To control how frequently WAL-G will check if Postgres is alive during the backup-push. If the check fails, backup-push terminates.

Examples:

• 0 - disable the alive checks (default value)
• 10s - check every 10 seconds
• 10m - check every 10 minutes