Add refcount on MemObj in blocked scenarios.

- Prevents destruction of MemObj while it may still be in use.
- Add UNRECOVERABLE to check whether object is deleted while having
dependencies, fix all problems is tests due to that fact.
- Fix special queue setting, clean interfaces.

Change-Id: I2a467e80df00ea1650decdcfa6866acf10b441f8

unit_tests/command_queue/enqueue_waitlist_tests.cpp

@@ -80,10 +80,10 @@ struct EnqueueWaitlistTest : public EnqueueWaitlistFixture,
     }
 
     void TearDown() override {
-        delete buffer;
-        delete bufferNonZeroCopy;
-        delete image;
-        delete imageNonZeroCopy;
+        buffer->decRefInternal();
+        bufferNonZeroCopy->decRefInternal();
+        image->decRefInternal();
+        imageNonZeroCopy->decRefInternal();
         EnqueueWaitlistFixture::TearDown();
     }