vtbackup: allow exiting if failing early #1058

Job	Run time
Set push variable	1s
Build and push vttestserver (mysql80)	1m 51s
Build and push lite (latest)	2m 6s
Build and push lite (percona80)	2m 14s
Build and push (bullseye, vtadmin)	1m 11s
Build and push (bullseye, vtorc)	37s
Build and push (bullseye, vtgate)	35s
Build and push (bullseye, vttablet)	39s
Build and push (bullseye, mysqlctld)	45s
Build and push (bullseye, mysqlctl)	35s
Build and push (bullseye, vtctl)	30s
Build and push (bullseye, vtctlclient)	31s
Build and push (bullseye, vtctld)	1m 3s
Build and push (bullseye, vtctldclient)	47s
Build and push (bullseye, logrotate)	30s
Build and push (bullseye, logtail)	23s
Build and push (bullseye, vtbackup)	32s
Build and push (bullseye, vtexplain)	37s
Build and push (bookworm, vtadmin)	1m 6s
Build and push (bookworm, vtorc)	26s
Build and push (bookworm, vtgate)	26s
Build and push (bookworm, vttablet)	39s
Build and push (bookworm, mysqlctld)	39s
Build and push (bookworm, mysqlctl)	32s
Build and push (bookworm, vtctl)	37s
Build and push (bookworm, vtctlclient)	40s
Build and push (bookworm, vtctld)	1m 29s
Build and push (bookworm, vtctldclient)	38s
Build and push (bookworm, logrotate)	35s
Build and push (bookworm, logtail)	24s
Build and push (bookworm, vtbackup)	41s
Build and push (bookworm, vtexplain)	27s
	24m 46s

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