Limit verbose log line on scheduled migration cancellation

[cwperks]

Description

Small change to only limit the Cancelling the migration process. log line if a scheduled migration exists.

This log line can be seen whenever an index is created regardless if scheduledMigration is null or non-null.

I ran into this log line when doing performance testing with the security plugin in scenarios where clusters contain a lot of indices and wrote a script to quickly create indices. This log line is pervasive when index creation is occurring.

Related Issues

Related to: #1183

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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