fix: catch DynamoDB Scan error when trying to scan nonexistent table or index

[spentakota]

When trying to integrate the vmware-go-kcl-v2 within one of our codebases a bug was identified by our one of our end to end tests that causes for a nil pointer error. This occurs when the rebalance() function is called when no checkpoint has been set for any of the shards so when syncLeases() is called the dynamoDB scan will return a scanOutput.items which is nil causing for the nil pointer error. This can be avoided if we check for any errors returned from the checkpointer.svc.Scan() call. According to the AWS documentation, the case being described will return a ResourceNotFoundExceptionerror which can now be caught and the function can return with the error with this fix.

[vmwclabot]

@spentakota, you must sign every commit in this pull request acknowledging our Developer Certificate of Origin before your changes are merged. This can be done by adding Signed-off-by: John Doe <john.doe@email.org> to the last line of each Git commit message. The e-mail address used to sign must match the e-mail address of the Git author. Click here to view the Developer Certificate of Origin agreement.

• Commit de47302 must be signed by spentakota@vmware.com

[vmwclabot]

@spentakota, you must sign every commit in this pull request acknowledging our Developer Certificate of Origin before your changes are merged. This can be done by adding Signed-off-by: John Doe <john.doe@email.org> to the last line of each Git commit message. The e-mail address used to sign must match the e-mail address of the Git author. Click here to view the Developer Certificate of Origin agreement.

• Commit 0d38d0a must be signed by spentakota@vmware.com

[vmwclabot]

@spentakota, you must sign every commit in this pull request acknowledging our Developer Certificate of Origin before your changes are merged. This can be done by adding Signed-off-by: John Doe <john.doe@email.org> to the last line of each Git commit message. The e-mail address used to sign must match the e-mail address of the Git author. Click here to view the Developer Certificate of Origin agreement.

• Commit 6578fdc must be signed by spentakota@vmware.com