feat(tablet): add uncompressed size to pb.Tablet

[NamanJain8]

• Add UncompressedBytes to pb.Tablet denoting the uncompressed size of tablet.
• Rename pb.Tablet.Space -> pb.Tablet.OnDiskBytes
• Simplify tablet size calculation as badger does not have internal keys now.

/state endpoint displays the tablet in format:

"post.body": {
          "groupId": 1,
          "predicate": "post.body",
          "force": false,
          "onDiskBytes": "40773239190",
          "remove": false,
          "readOnly": false,
          "moveTs": "0",
          "uncompressedBytes": "66824100606"
        },

Log in predicate move

Groups sorted by size: [{gid:2 size:0} {gid:1 size:73403748503}]

I1209 23:26:28.678858 2689798 tablet.go:215] size_diff 73403748503
I1209 23:26:28.679134 2689798 tablet.go:109] Going to move predicate: [comment.text], size: [ondisk: 13 GB, uncompressed: 19 GB] from group 1 to 2

---

This change is 

[manishrjain]

Reviewed 6 of 6 files at r1.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @NamanJain8 and @vvbalaji-dgraph)

---

worker/draft.go, line 1314 at r1 (raw file):

	var total int64
	tablets := make(map[string]*pb.Tablet)
	updateSize := func(pred string, onDiskSize int64, uncompressedSize int64) {

accept tinfo.

---

worker/draft.go, line 1349 at r1 (raw file):

		// Count the table only if it is occupied by a single predicate.
		if left.Attr == right.Attr {
			updateSize(left.Attr, int64(tinfo.OnDiskSize), int64(tinfo.UncompressedSize))

Just pass in tinfo.

[manishrjain]

humanize.IBytes

[danielmai]

Reviewed 5 of 5 files at r2.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @NamanJain8 and @vvbalaji-dgraph)