Fix occasional test failure in NetworkCrawlerTest

Previously if DataProvidersManagerTest ran before NetworkCrawlerTest it would
set data filters (which are static) that would interfere with
NetworkCrawlerTest. Now both tests clear filters.

src/test/java/org/orekit/data/DataProvidersManagerTest.java

@@ -27,13 +27,20 @@
 import java.util.regex.Pattern;
 
 import org.hipparchus.exception.DummyLocalizable;
+import org.junit.After;
 import org.junit.Assert;
 import org.junit.Test;
 import org.orekit.Utils;
 import org.orekit.errors.OrekitException;
 
 public class DataProvidersManagerTest {
 
+    @After
+    public void tearDown() {
+        // clear the filters so they don't change other tests
+        DataProvidersManager.getInstance().clearFilters();
+    }
+
     @Test
     public void testDefaultConfiguration() {
         System.setProperty(DataProvidersManager.OREKIT_DATA_PATH, getPath("regular-data"));

src/test/java/org/orekit/data/NetworkCrawlerTest.java

@@ -27,10 +27,17 @@
 
 import org.junit.Assert;
 import org.junit.Test;
+import org.junit.Before;
 import org.orekit.errors.OrekitException;
 
 public class NetworkCrawlerTest {
 
+    @Before
+    public void setUp() {
+        // Clear any filters that another test may have left
+        DataProvidersManager.getInstance().clearFilters();
+    }
+
     @Test(expected=OrekitException.class)
     public void noElement() throws MalformedURLException {
         File existing   = new File(url("regular-data").getPath());