Make unable to ping log messages appropriate level

The ping from an ssh connection checks in _check_remote_connectivity()
aren't necessarily expected to pass on the first attempt. However,
every time the ping was unsuccessful the method would log an
exception which is too severe a log for an expected error. This
commit uses a more appropriate log level for this case.

Change-Id: I8068fa85472259676acebd99b9d191065661e101
Merge "Make unable to ping log messages appropriate level"