Implement a capacity ratio on restore of tables

The schema:
```json
{
  "Table": {
    "AttributeDefinitions": [
      {
        "AttributeName": "id", 
        "AttributeType": "S"
      }
    ], 
    "ProvisionedThroughput": {
      "WriteCapacityUnits": 5, 
      "NumberOfDecreasesToday": 0, 
      "ReadCapacityUnits": 5
    }, 
    "TableSizeBytes": 0, 
    "TableName": "foobars", 
    "TableStatus": "ACTIVE", 
    "KeySchema": [
      {
        "KeyType": "HASH", 
        "AttributeName": "id"
      }
    ], 
    "ItemCount": 0, 
    "CreationDateTime": 1417464793.808
  }
}
```

On use:

```
$ python2.7 dynamodump.py -m restore -r local --host 127.0.0.1 --port 4567 --accessKey AKIAILPOISCA3646H5PQ --secretKey secret -s foobars -d foobars-bak --restoreCapacityRatio 0.3
INFO:root:foobars-bak table deleted!
INFO:root:Starting restore for foobars to foobars-bak..
INFO:root:Creating foobars-bak table with temp write capacity of 100
INFO:root:foobars-bak created.
INFO:root:Restoring data for foobars-bak table..
INFO:root:Processing 0001.json of foobars-bak
INFO:root:Updating foobars-bak table read capacity to: 2, write capacity to: 2
INFO:root:Restore for foobars to foobars-bak table completed. Time taken: 0:00:00

$ python2.7 dynamodump.py -m restore -r local --host 127.0.0.1 --port 4567 --accessKey AKIAILPOISCA3646H5PQ --secretKey secret -s foobars -d foobars-bak --restoreCapacityRatio 3
INFO:root:foobars-bak table deleted!
INFO:root:Starting restore for foobars to foobars-bak..
INFO:root:Creating foobars-bak table with temp write capacity of 100
INFO:root:foobars-bak created.
INFO:root:Restoring data for foobars-bak table..
INFO:root:Processing 0001.json of foobars-bak
INFO:root:Updating foobars-bak table read capacity to: 15, write capacity to: 15
INFO:root:Restore for foobars to foobars-bak table completed. Time taken: 0:00:00
```
@bchew maybe just --capacityRatio is a better name to be consistent with the rest, if you want to merge it, I can change it before