Add responses for timer commands

Bug: 154020729
Test: cert/run --host
   manual testing:
      out/host/linux-x86/bin/root-canal & sleep 1 && \
          python3 scripts/test_channel.py 6401 < scripts/start_and_stop
Change-Id: I0c9a5257e495af4174b3280cc969ebd449136cd9