[jmx-scraper] test all the possible ways to provide configuration

[SylvainJuge]

Currently, the JMX scraper tests are all using JVM system properties for configuration.

However, there are other ways to provide the configuration and they aren't tested end-to-end:

• standard input
• environment variables
• external properties file.

In order to test those, we should at least attempt to cover the minimal configuration for each of the 4 ways to configure it, we don't have to test every configuration option with every possible way to provide it.

In addition, doing that test work based on "test connnection" implemented in #1684 would be relevant as it allows to test the whole CLI program as the user would experience it. Work on this issue would then depend on #1684 to be merged though.