No KMS support

[jesdynf]

It'd be nice if we could pass KMS key IDs through to s3cmd.

       --server-side-encryption
              Specifies that server-side encryption will be used when  putting
              objects. [put, sync, cp, modify]

       --server-side-encryption-kms-id=KMS_KEY
              Specifies  the  key  id used for server-side encryption with AWS
              KMS-Managed Keys (SSE-KMS) when putting objects. [put, sync, cp,
              modify]

If I get enough of this working to make submitting a PR worthwhile, I'll try to do so. Thanks!

[jesdynf]

Oh, phooey. I dug deep enough into Duplicity to find out the issue -- it doesn't have KMS support. All it can do is default S3 encryption. I wanted hands-off automated passwords without plaintext storage --
which I did get, after a little magic with an intermediate password.

# create passphrase
touch /tmp/mypass
chmod 400 /tmp/mypass
openssl rand -base64 32 >> /tmp/mypass
aws s3 cp /tmp/mypass s3://$S3/Backup/passphrase.txt --sse aws:kms --sse-kms-key-id $KMS
rm /tmp/mypass

# fetch passphrase for use
PASSPHRASE=`aws s3 cp s3://$S3/Backup/passphrase.txt - --sse aws:kms --sse-kms-key-id $KMS`

Sorry to bother you!