unit/integration tests for multi-gpu data analyzer

[wyli]

Is your feature request related to a problem? Please describe.

with #6202 the module still lacks testing in a multi-gpu environment

cc @heyufan1995

[wyli]

the test is actually running for multi-gpu

MONAI/tests/test_auto3dseg.py

Lines 203 to 204 in 6b7b1e7

	analyser = DataAnalyzer(
	self.datalist_file, self.dataroot_dir, output_path=self.datastat_file, label_key=label_key, device="cuda"