tests: clean DB container after tests

Cleans up running DB container when some pytest segfaults.

Removes forgotten `import wdb` statement that was breaking running tests
when only the `.[tests]` installation target is called to set up the
test prerequisites.

Closes reanahub/reana#755.

run-tests.sh

@@ -85,6 +85,7 @@ check_sphinx () {
 check_pytest () {
     clean_old_db_container
     start_db_container
+    trap clean_old_db_container SIGINT SIGTERM SIGSEGV ERR
     python setup.py test
     stop_db_container
 }

tests/test_deleter.py

@@ -10,8 +10,6 @@
 import pathlib
 import uuid
 
-import wdb
-
 from reana_server.deleter import Deleter, InOrOut
 from reana_commons.workspace import iterdir, is_directory, walk