Give units when reporting large tiles

[pnorman]

Right now large tiles are reported like handle_map_layer_zxy.go:177: tile z:8, x:40, y:86 is rather large - 541058 but it doesn't say if that's bytes, kb, or something else.

[stvno]

the units are not even consistent, in the output below they seem to be ranging from 1-9M

2018-09-05 16:45:26 [INFO] handle_map_layer_zxy.go:177: tile z:8, x:132, y:85 is rather large - 9176148: 
2018-09-05 16:45:28 [INFO] handle_map_layer_zxy.go:177: tile z:8, x:131, y:85 is rather large - 8938648: 
2018-09-05 16:45:40 [INFO] handle_map_layer_zxy.go:177: tile z:8, x:132, y:83 is rather large - 1255507: 
2018-09-05 16:45:44 [INFO] handle_map_layer_zxy.go:177: tile z:8, x:132, y:84 is rather large - 1933525: 
2018-09-05 16:45:49 [INFO] handle_map_layer_zxy.go:177: tile z:8, x:131, y:84 is rather large - 2484144: 

Whereas the files on disk are:

8/131:
-rw-r--r-- 1 steven steven 2484144 sep  5 16:45 84
-rw-r--r-- 1 steven steven  893864 sep  5 16:45 85

8/132:
-rw-r--r-- 1 steven steven 1255507 sep  5 16:45 83
-rw-r--r-- 1 steven steven 1933525 sep  5 16:45 84
-rw-r--r-- 1 steven steven  917614 sep  5 16:45 85

thus ranging from 897K - 2.4M

[gdey]

It's reporting in bytes.
https://github.com/go-spatial/tegola/blob/master/server/handle_map_layer_zxy.go#L177

We can make it more readable by converting it all to Kb.

// check for tile size warnings
	if len(pbyte) > MaxTileSize {
		log.Infof("tile z:%v, x:%v, y:%v is rather large - %0.2fKb", req.z, req.x, req.y, len(pbyte)/1024)
	}