Added aws:kms mode to get/put/post operations.

Added aws:kms mode to get/put/post operations.

Refactored to export selection of encryption to rgw/rgw_crypt.h/cc
Added quick exit to from_base64 when string_ref is empty.
Fixed POST logic, so aws encryption can also be applied to objects created from web forms
Extended KeystoneService with barbican user configuration.
Keystone provides token, Barbican provides secret.
Added option rgw_barbican_url.

Signed-off-by: Adam Kupczyk <akupczyk@mirantis.com>
Signed-off-by: Radoslaw Zarzynski <rzarzynski@mirantis.com>