Update system-rules dependency from 1.12.1 to 1.15.0

com.github.stefanbirkner:system-rules releases are now up to 1.15.0. We should update our dependency from 1.12.1 to 1.15.0.

System-Rules is a library of JUnit Rules used in UnitTests, IntegrationTests and DistributedTests for controlling System properties, stdout, stderr, etc.