Blacklist PyQgsDBManagerGpkg test

The test consistently segfaults on Travis, but run fine locally,
normally or under Valgrind.
Trying to run it under Valgrind on Travis runners does not succeed:
https://travis-ci.org/rouault/Quantum-GIS/builds/168674938

So blacklist for now

ci/travis/linux/qt4/script.sh

@@ -24,4 +24,4 @@ if [ "${TRAVIS_PULL_REQUEST}" != "false" ]; then
   chmod -R ugo-w ~/.ccache
 fi
 
-xvfb-run ctest -V -E 'qgis_openstreetmaptest|qgis_wcsprovidertest|qgis_ziplayertest' -S ./qgis-test-travis.ctest --output-on-failure
+xvfb-run ctest -V -E 'qgis_openstreetmaptest|qgis_wcsprovidertest|qgis_ziplayertest|PyQgsDBManagerGpkg' -S ./qgis-test-travis.ctest --output-on-failure

ci/travis/linux/qt5/blacklist.txt

@@ -16,3 +16,4 @@ qgis_composermapgridtest
 qgis_composerutils
 ProcessingGrass7AlgorithmsImageryTest
 ProcessingGrass7AlgorithmsRasterTest
+PyQgsDBManagerGpkg