Use Maven profiles to handle different versions of TestNG

[sbesson]

Superseded #24 - see also ome/ome-common-java#88

For JDK8, bump org.testng:testng to the last supported release for this version i.e. 7.5
For JDK11+, bump org.testng:testng to the latest release 7.9.0

[sbesson]

@melissalinkert in https://github.com/ome/bioformats, I noticed that org.testng:testng is declared as a dependency for each component and the version of the dependency is declared the properties tag in the top-level POM.

Rather than duplicating the profile code for each component, 9b981f8 explores an option to maintain this semantics and make the value of testng.version profile-activated depending on the JDK version. I'll wait to hear your thoughts before opening a similar change against Bio-Formats

[melissalinkert]

Setting just testng.version based on the profile makes sense to me, especially in ome/bioformats.

I'm fine with either this or the approach in ome/ome-common-java#88 for the low-level repositories, though, so totally up to you if want to leave the other similar pull requests as-is or use the version property approach across the board.