tests: kdump.crash enable more debugging in kdump service

Recent kdump updates started to fail without any error, so this
will increase the verbosity of the kdump service.
This will increase the logs size but logs are discarded on
successful tests so that's fine.

See rhkdump/kdump-utils#15 (comment)

tests/kola/kdump/crash/config.bu

@@ -12,3 +12,8 @@ systemd:
   units:
     - name: kdump.service
       enabled: true
+      dropins:
+        - name: debug.conf
+          contents: |
+            [Service]
+            Environment="debug=1"