API Endpoint - Check History

Add an endpoint to get the last check time and exit code of all checks for a node. Add the client timestamp to a new redis key. Add an API endpoint to iterate over checks, and query different keys. Marshall to one JSON response.

Request
---
<pre>
curl -L 'http://localhost:4567/clients/namenode001/history'
</pre>

Sample output
<pre>
[
    {
        "check": "namenode_health",
        "executed": "1363217459",
        "status": "0"
    },
    {
        "check": "namenode_fsck",
        "executed": "1363217459",
        "status": "0"
    },
    {
        "check": "namenode_checkpoint",
        "executed": "1363217519",
        "status": "127"
    },
    {
        "check": "secondarynamenode_alive",
        "executed": "1363217519",
        "status": "0"
    },
    {
        "check": "namenode_alive",
        "executed": "1363217519",
        "status": "0"
    },
    {
        "check": "namenode_fs_state",
        "executed": "1363217519",
        "status": "0"
    }
]
</pre>