fix(upgrade): make sure trap will throw no errors

[starbops]

Signed-off-by: Zespre Chang zespre.chang@suse.com

IMPORTANT: Please do not create a Pull Request without creating an issue first.

Problem:

When upgrading with the same ISO, the cleanup trap in the upgrade_os will throw out an error that triggers the post-drain to retry again. This is because the line:

[[ -n "$NEW_OS_SQUASHFS_IMAGE_FILE" ]] && \rm -vf "$NEW_OS_SQUASHFS_IMAGE_FILE"

will short-circuit with a non-zero return code if the variable is not set.

Solution:

A trap should never exit with a non-zero return code, all cases should be handled carefully.

Related Issue:

#3175

Test plan:

1. Create a cluster with master ISO after v1.1.1-rc1
2. Upgrade to the same ISO again
3. Check if the post-drain job ended successfully

[guangbochen]

LGTM, thanks.

[futuretea]

LGTM

[bk201]

LGTM