avoid crawler to obtain a thread with a remanant context

[cmangeat]

as team programmed

[cmangeat]

@josegar74 @juanluisrp as said before.

[cmangeat]

Relates to #2827

[josegar74]

@fxprunayre as you worked in https://github.com/geonetwork/core-geonetwork/pull/2859/files#diff-104af28d3030368a152d64430caa944b, would you mind to take a look to the fix.

We tested using a threadpool size of 1 to reproduce easily the issue and without the fix the problem described by @cmangeat occurred, while with the fix worked fine.

Checked other cases, like using the new API services or Jeeves services not handled as a crawler requests and seemed fine as the Jeeves ServiceManager/new API managed to update the proper ServiceContext in the request threadpool.

[josegar74]

@cmangeat can you make the PR to master branch instead of 3.4.x? We discussed to apply fixes first to master and the cherry-pick to 3.4.x. I'll manage about this, thanks.

[juanluisrp]

Any idea about why the test are failing in Travis?

Running jeeves.server.dispatchers.ServiceManagerIntegratedTest
Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 56.402 sec <<< FAILURE! - in org.fao.geonet.DataManagerWorksWithoutTransactionIntegrationTest
testDataManagerCutpoints(org.fao.geonet.DataManagerWorksWithoutTransactionIntegrationTest)  Time elapsed: 15.088 sec  <<< FAILURE!
java.lang.AssertionError: null
	at org.junit.Assert.fail(Assert.java:92)
	at org.junit.Assert.assertTrue(Assert.java:43)
	at org.junit.Assert.assertTrue(Assert.java:54)
	at org.fao.geonet.GeonetTestFixture.assertRequiredSchemas(GeonetTestFixture.java:222)
	at org.fao.geonet.GeonetTestFixture.initSchemaManager(GeonetTestFixture.java:215)
	at org.fao.geonet.GeonetTestFixture.setup(GeonetTestFixture.java:138)
	at org.fao.geonet.AbstractCoreIntegrationTest.setup(AbstractCoreIntegrationTest.java:145)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
...

Running org.fao.geonet.kernel.AccessManagerTest
Tests run: 2, Failures: 0, Errors: 2, Skipped: 0, Time elapsed: 2.834 sec <<< FAILURE! - in org.fao.geonet.kernel.AccessManagerTest
testIsIntranetBackwardCompatibility(org.fao.geonet.kernel.AccessManagerTest)  Time elapsed: 2.192 sec  <<< ERROR!
java.lang.NullPointerException: null
	at org.fao.geonet.kernel.SchemaManager.configureFrom(SchemaManager.java:171)
	at org.fao.geonet.GeonetTestFixture.configureNewSchemaManager(GeonetTestFixture.java:189)
	at org.fao.geonet.GeonetTestFixture.setup(GeonetTestFixture.java:158)
	at org.fao.geonet.AbstractCoreIntegrationTest.setup(AbstractCoreIntegrationTest.java:145)
...