Add new maven profile for PR tests

We already have 2 maven profiles:

• full build - builds and tests everything, including contrib, c-client
• java-build - only builds and tests java server, client and recipes

For the PR test run, we should add a third one, that excludes contrib from the full-build profile.

As Enrico suggested, we could have seperate jobs for testing C and Java:

• test java -> run with java-build profile
• test C -> run with newly added c-client profile