Testing function for chunked memory pool test

[LWisteria]

Theare are many same parts for memory pool test. e.g.

clpy/tests/clpy_tests/opencl_tests/test_carray.py

Lines 12 to 17 in 65143ed

	# create chunk and free to prepare chunk in pool
	self.pool = clpy.backend.memory.SingleDeviceMemoryPool()
	clpy.backend.memory.set_allocator(self.pool.malloc)
	self.pooled_chunk_size = clpy.backend.memory.subbuffer_alignment * 2
	self.tmp = self.pool.malloc(self.pooled_chunk_size)
	self.pool.free(self.tmp.buf, self.pooled_chunk_size, 0)

Those causes maintainance risk. Unify them into a function of testing tool.