workarounds for dhclient and cassandra

- fix dhclient issue with multiple instances for the same interface
- reduce 'max_heap_size' for cassandra in order to lower memory
  footprint
diff --git a/tcp_tests/templates/underlay/mk22-qa-lab01--user-data-cfg01.yaml b/tcp_tests/templates/underlay/mk22-qa-lab01--user-data-cfg01.yaml
index 31f60a7..c90e6ad 100644
--- a/tcp_tests/templates/underlay/mk22-qa-lab01--user-data-cfg01.yaml
+++ b/tcp_tests/templates/underlay/mk22-qa-lab01--user-data-cfg01.yaml
@@ -48,7 +48,7 @@
    ########################################################
 
   write_files:
-   - path: /etc/network/interfaces.d/99-tcp-tests.cfg
+   - path: /etc/network/interfaces
      content: |
           auto ens3
           iface ens3 inet dhcp