Handle "Not implemented" error codes in functional test

[kannappanr]

In s3 gateway mode, some calls return "not implemented".
We should handle the situation gracefully, and not fail basically.

status: "NA"
alert: "Not Implemented"

Here is an example error.
Please look at the error part of the entry

{"alert":"","args":{"destination":{},"sources":[{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"],"X-Amz-Copy-Source-Range":["bytes=0-5242879"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}},{"Headers":{"X-Amz-Copy-Source":["minio-go-testpqymyww039cgzqvvy/srcObject"],"X-Amz-Copy-Source-If-Match":["2b5c91ad399409ec9b409b66f5bb00fb"]}}]},"duration":5218,"error":"Error in upload-part-copy - A header you provided implies functionality that is not implemented","function":"ComposeObject(destination, sources)","message":"ComposeObject failed","name":"minio-go","status":"fail"}