Add x-amz-storage-class support (#5295)

This adds configurable data and parity options on a per object
basis. To use variable parity

- Users can set environment variables to cofigure variable
parity

- Then add header x-amz-storage-class to putobject requests
with relevant storage class values

Fixes #4997

cmd/xl-v1-healing-common_test.go

@@ -364,7 +364,8 @@ func TestDisksWithAllParts(t *testing.T) {
 	}
 
 	partsMetadata, errs := readAllXLMetadata(xlDisks, bucket, object)
-	if reducedErr := reduceReadQuorumErrs(errs, objectOpIgnoredErrs, xl.readQuorum); reducedErr != nil {
+	readQuorum := len(xl.storageDisks) / 2
+	if reducedErr := reduceReadQuorumErrs(errs, objectOpIgnoredErrs, readQuorum); reducedErr != nil {
 		t.Fatalf("Failed to read xl meta data %v", reducedErr)
 	}