set classifier

[jburel]

The build creates 2 jars; one containing the testing code and one containing the main code.
When the jars are built from the super-build. the content of the testing jar is copying into the main jar
i.e. omero-common.jar contains the classes from omero-common-test.jar leading to a failure of the build.
This PR adds a classifier preventing this problem to occur. This is a workaround since an extra "tests" jar is created

--exclude

[sbesson]

The addition of a classifier makes sense.

However, it raises two questions:

• why tests while the suffix is -test
• in general, is there a reason to keep 2 separate artifacts with the same version or should the test JAR really be another outcome of omero-common with the test[s] classifier (like Javadoc or sources)?

The second bullet point certainly wider implications in terms of all the downstream components (omero-server/omero-blitz via testImplementation and OmeroJava via test.xml) but I think both Gradle and Ivy have built-in way to specify classifiers.

[jburel]

I will need to go back to it since the packaging is done with our upstream repo.

[sbesson]

Following the component release, this PR broke the daily CI build - see https://merge-ci.openmicroscopy.org/jenkins/job/OMERO-build/1487/console

00:57:42 /home/omero/workspace/OMERO-build/src/components/tools/OmeroJava/test/integration/delete/AdditionalDeleteTest.java:14: error: package ome.testing does not exist
00:57:42 import ome.testing.ObjectFactory;

Added an exclude comment to the description which sufficed to fix the build.

I suspect the logic have been working previously because a 5.6.1-SNAPSHOT artifact without the classifier was present in the build environment and could be used by the build syste,.
If we re-include the proposed changed, we will likely need to tackle the consumption of the new artifact by downstream components as discussed in #40 (review).