[master-test] TestDumpStacksOnRpcQueueOverflow is not relevant on macOS
[master-test] TestDumpStacksOnRpcQueueOverflow is not relevant on macOS

As Will noticed, the TestDumpStacksOnRpcQueueOverflow scenario always
fails on macOS since the stack trace dumping is not supported there.
This patch simply moves the TestDumpStacksOnRpcQueueOverflow scenario
under '#ifndef __APPLE__ ... #endif' macro.

This is a follow-up for 96b3b63a48c270a77819e6fc80d1dfdb381a0df7.

Change-Id: Id6e1424a37628537f45b6cda7fd9b7e06101e53e
Reviewed-on: http://gerrit.cloudera.org:8080/9720
Tested-by: Kudu Jenkins
Reviewed-by: Will Berkeley <c74686ab413a71926fc1bc9d16ebfa30e619336a@gmail.com>

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