rgw: s3: awsv4 drop special handling for x-amz-credential

rgw: s3: awsv4 drop special handling for x-amz-credential

While s3 docs mention that every byte must be urlencoded, they are relaxed in
its implementation, when testing this behaviour on aws s3 itself, they seem to
be relaxed in handling aws credentials of the form

X-Amz-Credential=access1/20180817T123456Z/us-east-1...

wherein

X-Amz-Credential=access1%2F2018...

is expected. This allows for clients requesting the urls in both forms to
succeed as aws s3 does at the moment

Fixes: http://tracker.ceph.com/issues/26965
Signed-off-by: Abhishek Lekshmanan <abhishek@suse.com>
(cherry picked from commit 25e1d2a32074254e9ebd780f3a41b2ff6469370f)