Allow snapshot repositories in integration tests

Update CLI SampleIntegrationTests to no longer disable snapshot repos.
Polish pom.xml

Aplly consistent formatting, drop JDK 8 support and cleanup repo
locations to use spring.io.
Create CliTester JUnit @Rule

Extract logic from SampleIntegrationTests into a reusable JUnit @Rule.
Merge remote-tracking branch 'origin/master' into crashub
Fixed handling for filesystem refresh behaviour useful for command creation and debugging
Added metrics command to display Spring Boot metrics