Change sys.exit(1) to raise in autoscaler update ssh_cmd

[hartikainen]

What do these changes do?

Changes sys.exit(1) to raise in autoscaler update ssh_cmd, in order to avoid premature exit on updater uptime command. Uptime command sometimes expects an error and doing sys.exit() prevents it from running correctly.

Related issue number

#5265

Linter

• I've run scripts/format.sh to lint the changes in this PR.

[hartikainen]

cc @richardliaw

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[richardliaw]

exit_on_fail=True

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[richardliaw]

@hartikainen can you review and merge? Tests should pass this time around.

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[ericl]

Let's hold this since the release is so near (I have a straightforward revert here: #5299)

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