S3 api: Ignore encoding in xml body (#6953)
S3 api: Ignore encoding in xml body (#6953)

One user reported having discovered the following error:

API: SYSTEM()
Time: 20:06:17 UTC 12/06/2018
Error: xml: encoding "US-ASCII" declared but Decoder.CharsetReader is nil
1: cmd/handler-utils.go:43:cmd.parseLocationConstraint()
2: cmd/auth-handler.go:250:cmd.checkRequestAuthType()
3: cmd/bucket-handlers.go:411:cmd.objectAPIHandlers.PutBucketHandler()
4: cmd/api-router.go100cmd.(objectAPIHandlers).PutBucketHandler-fm()
5: net/http/server.go:1947:http.HandlerFunc.ServeHTTP()

Hence, adding support of different xml encoding. Although there
is no clear specification about it, even setting "GARBAGE" as an xml
encoding won't change the behavior of AWS, hence the encoding seems
to be ignored.

This commit will follow that behavior and will ignore encoding field
and consider all xml as utf8 encoded.
donatello/minio,minio/minio,harshavardhana/minio,fwessels/minio,krishnasrinivas/minio,aead/minio,donatello/minio,vadmeste/minio,harshavardhana/minio,NitishT/minio,krishnasrinivas/minio,jimjag/minio,krisis/minio,balamurugana/minio,balamurugana/minio,krisis/minio,fwessels/minio,fwessels/minio,jimjag/minio,harshavardhana/minio,aead/minio,harshavardhana/minio,aead/minio,krishnasrinivas/minio,aead/minio,harshavardhana/minio,aead/minio,minio/minio,jimjag/minio,aead/minio,fwessels/minio,vadmeste/minio,NitishT/minio,harshavardhana/minio,harshavardhana/minio,harshavardhana/minio,NitishT/minio,aead/minio,krishnasrinivas/minio,aead/minio,jimjag/minio,NitishT/minio