[FLINK-35295][mysql] Improve jdbc connection pool initialization failure message #496

Job	Run time
license_check	3m 15s
compile_and_test (8, core)	2m 9s
compile_and_test (8, pipeline_connectors)	4m 23s
compile_and_test (8, mysql)	35m 36s
compile_and_test (8, postgres)	23m 13s
compile_and_test (8, oracle)	20m 9s
compile_and_test (8, mongodb)	22m 34s
compile_and_test (8, sqlserver)	11m 44s
compile_and_test (8, tidb)	2m 6s
compile_and_test (8, oceanbase)	4m 5s
compile_and_test (8, db2)	19m 40s
compile_and_test (8, vitess)	2m 32s
compile_and_test (8, e2e)	1h 6m 49s
	3h 38m 15s

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