The test case
testIndividualProjectBuilds_WithManyProjects_ProjectRelaxedRule() in
ParallelBuildChainTest fails randomly (in I-Builds) because not all jobs
that are supposed to run build operations are scheduled and started in
time. Since the test is not supposed to validate that a specific number
of jobs can be started, the number of jobs/builds to be spawned must
actually not be as high as currently defined. This change reduces the
number of projects in the test case to avoid random test failures while
keeping expressiveness of the test case.

Fixes https://github.com/eclipse-platform/eclipse.platform/issues/825