azureblob and fstests - Modify integration tests to include new

optional setting to test SetTier on only few supported tiers.

Remove unused optional interface ListTiers and backend and internal tests

backend/azureblob/azureblob_test.go

@@ -14,7 +14,8 @@ import (
 // TestIntegration runs integration tests against the remote
 func TestIntegration(t *testing.T) {
 	fstests.Run(t, &fstests.Opt{
-		RemoteName: "TestAzureBlob:",
-		NilObject:  (*azureblob.Object)(nil),
+		RemoteName:  "TestAzureBlob:",
+		NilObject:   (*azureblob.Object)(nil),
+		TiersToTest: []string{"Hot", "Cool"},
 	})
 }