Log additional details during `downloadUpdate()` step

[joshtrichards]

• Periodic progress (i.e. every 30s we log how things are progressing)
• Final log entry during step with a summary:
  • Avg download speed
  • DNS lookup time
  • HTTPS handshake time
  • Connect-to-first-byte transferred time
  • v6 versus v4
  • maybe the curl/libcurl version too

We can get all of this via curl_getinfo()

[joshtrichards]

Duplicate of #188 (well, logging versus indicating to operator in real-time via web/cli mode)