put key requests against moto server fail using Java AWS SDK

[MChamberlin]

An Exception is raised when writing keys to the moto S3 server using the Java AWS SDK:

com.amazonaws.AmazonClientException: Unable to complete transfer: null
	at com.amazonaws.services.s3.transfer.internal.AbstractTransfer.unwrapExecutionException(AbstractTransfer.java:277)
	at com.amazonaws.services.s3.transfer.internal.AbstractTransfer.rethrowExecutionException(AbstractTransfer.java:261)
	at com.amazonaws.services.s3.transfer.internal.AbstractTransfer.waitForCompletion(AbstractTransfer.java:103)
Caused by: java.lang.NullPointerException: null
	at com.amazonaws.util.BinaryUtils.fromHex(BinaryUtils.java:61)
	at com.amazonaws.services.s3.AmazonS3Client.putObject(AmazonS3Client.java:1441)
	at com.amazonaws.services.s3.transfer.internal.UploadCallable.uploadInOneChunk(UploadCallable.java:135)
	at com.amazonaws.services.s3.transfer.internal.UploadCallable.call(UploadCallable.java:127)
	at com.amazonaws.services.s3.transfer.internal.UploadMonitor.call(UploadMonitor.java:129)
	at com.amazonaws.services.s3.transfer.internal.UploadMonitor.call(UploadMonitor.java:50)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

The key is actually written correctly and I can access it using the python boto client. I've identified the issue as a mis-labeled field in the HTTP response for key PUT requests. The problem (and solution) are basically identical to that described in this Stack Overflow post. One of the returned metadata fields is named etag in moto, while the correct field name expected by the Java AWS SDK client is ETag.

[MChamberlin]

I've submitted a PR for the fix here.

[spulec]

Fixed with #855