PHOENIX-7826 MetadataGetTableReadLockIT wait for coprocessor swap to land

[apurtell]

The testBlockedReadDoesNotBlockAnotherRead test installs a BlockingMetaDataEndpointImpl coprocessor on SYSTEM.CATALOG and expects a worker thread's query to hit it and signal a latch the main thread is waiting on, but TestUtil.addCoprocessor() only updates the master TableDescriptor and doesn't wait for region servers to reopen the region with the new coprocessor, so if the query reaches the old MetaDataEndpointImpl first the latch is never signaled and the main thread hangs until the Surefire/Failsafe fork times out. The fix is to add a helper that polls each SYSTEM.CATALOG region's coprocessor host (via findCoprocessor for up to 10 seconds and call it after addCoprocessor so the coprocessor swap is guaranteed visible before the worker thread starts.