Fix tests.

module_build_service/utils/general.py

@@ -457,7 +457,11 @@ def get_local_releasever():
     Returns the $releasever variable used in the system when expanding .repo files.
     """
     # Import DNF here to not force it as a hard MBS dependency.
-    import dnf
+    try:
+        import dnf
+    except:
+        log.warning("Cannot import DNF module, releasever not set in Mock config.")
+        return ""
     dnf_base = dnf.Base()
     return dnf_base.conf.releasever