ktesting: support multi-line result from AnyToStringHook

[pohly]

What this PR does / why we need it:

When the hook returns a multi-line string, for example a YAML dump, then continuing directly after the end of that string with the next key/value pair was a bit hard to read:

dra_manager.go:288: I0129 17:41:55.722711] scheduler: Finished GatherAllocatedState allocatedDevices=<struct { Count int "json:\"count\""; Devices []string "json:\"devices\"" }>:
  ...
               - testdra-all-usesallresources-qzvpg.driver/worker-7/worker-7-device-005 err=<nil>: nil

In this example, allocatedDevices was passed by the hook to gomega.Format which added the type description and then produced YAML. With this change, such output becomes:

dra_manager.go:288: I0129 17:41:55.722711] scheduler: Finished GatherAllocatedState allocatedDevices=<
	<struct { Count int "json:\"count\""; Devices []string "json:\"devices\"" }>:
	...
 	              - testdra-all-usesallresources-qzvpg.driver/worker-7/worker-7-device-005
 > err=<nil>: nil

Which issue(s) this PR fixes:

kubernetes/kubernetes#136268 (comment)

Special notes for your reviewer:

Release note:

ktesting: support multi-line result from AnyToStringHook by applying the normal multi-line escaping.

/assign @tallclair

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