Add more tests for caliper worker #448

Job	Run time
dci-lint / DCI-Lint	28s
unit-tests / Unit Tests (18.x)	43s
unit-tests / Unit Tests (20.x)	34s
integration-tests / Check for changes	2s
coverage / Coverage Reports (caliper-core)	6s
coverage / Coverage Reports (caliper-fabric)	4s
coverage / Coverage Reports (generator-caliper)	9s
integration-tests / Integration Tests (fabric, 18.x)	13m 38s
integration-tests / Integration Tests (fabric, 20.x)	13m 54s
integration-tests / Integration Tests (ethereum, 18.x)	4m 24s
integration-tests / Integration Tests (ethereum, 20.x)	4m 29s
integration-tests / Integration Tests (besu, 18.x)	6m 43s
integration-tests / Integration Tests (besu, 20.x)	6m 41s
integration-tests / Integration Tests (generator, 18.x)	5m 26s
integration-tests / Integration Tests (generator, 20.x)	5m 25s
	1h 2m 46s

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