Better error message when node not synced

[WhoSoup]

My local mainnet node's first pass was 100% but second pass was lagging behind 3 blocks (I started it recently), which resulted in the following set of messages:

time="2019-10-06T15:29:22+02:00" level=debug msg=synced height=213120 took=80.0045ms
time="2019-10-06T15:29:22+02:00" level=debug msg=synced height=213121 took=104.006ms
time="2019-10-06T15:29:22+02:00" level=debug msg=synced height=213122 took=86.0049ms
time="2019-10-06T15:29:22+02:00" level=debug msg=synced height=213123 took=106.0061ms
time="2019-10-06T15:29:22+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:27+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:32+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:37+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:42+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:48+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:53+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:29:58+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:03+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:08+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:13+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:18+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:23+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:28+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:33+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:38+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:43+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:48+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:53+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:30:58+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:03+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:08+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:13+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:18+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:23+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:28+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:33+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:38+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:43+02:00" level=error msg="failed to sync height" error="jsonrpc2.Error{Code:-32008, Message:"Object not found"}" height=213124
time="2019-10-06T15:31:48+02:00" level=debug msg=synced height=213124 took=68.0039ms
time="2019-10-06T15:31:48+02:00" level=debug msg=synced height=213125 took=91.0052ms
time="2019-10-06T15:31:58+02:00" level=debug msg=synced height=213126 took=81.0047ms

If the height is available but the data is not, we should print out a better message. something like "data not yet downloaded on node", OR we could be using entryblockheight instead of directoryblockheight