[test] Avoid usage of lgc TestCase

Use cubicweb's BaseTestCase since we use datapath() method.
Drop usage of non-standard set_description() method and use subtests.

test/unittest_lcsv.py

@@ -15,7 +15,7 @@
 # You should have received a copy of the GNU Lesser General Public License along
 # with this program. If not, see <http://www.gnu.org/licenses/>.
 
-from logilab.common.testlib import TestCase
+from cubicweb.devtools.testlib import BaseTestCase as TestCase
 
 from cubicweb_skos import lcsv
 from cubicweb_skos.rdfio import unicode_with_language as ul

test/unittest_rdfio.py

@@ -18,7 +18,8 @@
 import os
 from tempfile import NamedTemporaryFile
 
-from logilab.common.testlib import TestCase, require_module
+from cubicweb.devtools.testlib import BaseTestCase as TestCase
+from logilab.common.testlib import require_module
 
 from cubicweb.devtools import testlib
 
@@ -232,8 +233,8 @@ class RDFGraphTCMixIn(object):
     def test_load_dump_roundtrip(self):
         # XXX other formats fail, but sounds due to the underlying lib
         for rdf_format in ('xml',):  # 'n3', 'nt'):
-            self.set_description('testing roundtrip for the %s format' % rdf_format)
-            self.assertRoundTrip(rdf_format)
+            with self.subTest(rdf_format):
+                self.assertRoundTrip(rdf_format)
 
     def assertRoundTrip(self, rdf_format='xml'):
         with NamedTemporaryFile(delete=False) as fobj: