Don't skip tests jar generation during tests

[neykov]

When passed -PIntegration tests jars are not getting built on purpose. This causes build failures down the road where the missing tests-jar is a dependency in another module.

Initially introduced in apache/incubator-brooklyn@dbda0be?w=1 without any details on why it's needed.

[neykov]

Interesting, but unrelated failure:

Tests run: 1663, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 270.277 sec <<< FAILURE! - in TestSuite
testConcurrentCallToManageForbidden(org.apache.brooklyn.core.entity.proxying.ApplicationBuilderOverridingTest)  Time elapsed: 20.044 sec  <<< FAILURE!
java.lang.AssertionError: expected [true] but found [false]
    at org.testng.Assert.fail(Assert.java:94)
    at org.testng.Assert.failNotEquals(Assert.java:494)
    at org.testng.Assert.assertTrue(Assert.java:42)
    at org.testng.Assert.assertTrue(Assert.java:52)
    at org.apache.brooklyn.core.entity.proxying.ApplicationBuilderOverridingTest$11.doBuild(ApplicationBuilderOverridingTest.java:205)
    at org.apache.brooklyn.core.entity.factory.ApplicationBuilder.manage(ApplicationBuilder.java:219)
    at org.apache.brooklyn.core.entity.proxying.ApplicationBuilderOverridingTest.testConcurrentCallToManageForbidden(ApplicationBuilderOverridingTest.java:230)

/cc @aledsage

[ahgittin]

LGTM