Tolerate network errors in pingtest retry logic

Tolerate network errors in pingtest retry logic

We use ping -w <deadline> -c <count>. This will ping every second until
<count> replies are received, or <deadline> is reached, or a network error occurs.

With the current retry logic a network error will result in a short tight loop
instead of waiting for the network to come up.

This change reduces the deadline to 10s, but sleeps 60s between retries.

Change-Id: Ib00cff6f843c04a00737b40e3ef3d1560d6e6d2d
Related-bug: #1680167