provider/aws: Report available sooner for RDS

[catsby]

Implements option number 2 from #1097.

In order to speed up our creation time, but still not progress until we can safely do so, we report an available status for the database if we're waiting on a backup, and our status is backing-up. This state is reached once the database is up and running, but AWS won't report available until the backup is done.

The output for a database with no backups:

2015/05/19 15:05:26 [DEBUG] DB Instance status: creating
2015/05/19 15:05:26 [TRACE] Waiting 10s before next try
2015/05/19 15:05:36 [DEBUG] DB Instance describe configuration: <truncated>
2015/05/19 15:05:36 [DEBUG] DB Instance status: available
2015/05/19 15:05:36 [DEBUG] DB Instance describe configuration: <truncated>
<moving on>

And with a backup_retention_period > 1:

2015/05/19 15:14:15 [DEBUG] DB Instance status: creating
2015/05/19 15:14:15 [TRACE] Waiting 10s before next try
2015/05/19 15:14:25 [DEBUG] DB Instance describe configuration: <truncated>
2015/05/19 15:14:25 [DEBUG] DB Instance status: backing-up
2015/05/19 15:14:25 [DEBUG] DB Instance describe configuration: <truncated>
2015/05/19 15:14:26 [DEBUG] root: eval: *terraform.EvalWriteState
<moving on>

... and then we go about our business.

The decimation on instance backups (here) mentions some I/O caveats:

During the backup window, storage I/O may be suspended while your data is being backed up and you may experience elevated latency. This I/O suspension typically lasts for the duration of the snapshot.

It's probably acceptable in our case.

cc @radeksimko and @phinze for thoughts

We also add extra [DEBUG] here so people can see the status of the operation, e.g. creating, backing-up etc

[phinze]

Anythings that makes RDS interactions marginally faster is tops in my book. LGTM

[catsby]

Unfortunately as is, this conflicts with #1946 , because a replica cannot be created from a database that is in backing-up state.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.