Add statsd metric for looking up /.well-known/browserid

fixes #1704
report success and failure cases separately for fetch_well_known and deep_fetch_well_known statsd metrics.
Send along the start time and timestamp with the .well-known statsd metrics.
Place elapsed time into its own field in the log

```
{"elapsed":246,"level":"info","message":"elapsed_time.deep_fetch_well_known.error","timestamp":"2013-10-16T13:24:43.255Z"}
```
Merge pull request #3969 from shane-tomlinson/issue-1704-address-info-statsd

Add statsd metric for looking up /.well-known/browserid