fs: validate filesystem path argument properly. (#3470)

FS should fail for invalid paths like

 - file:///
 - ftp://
 - http://

cmd/server-main_test.go

@@ -17,6 +17,7 @@
 package cmd
 
 import (
+	"errors"
 	"flag"
 	"net/http"
 	"os"
@@ -182,15 +183,25 @@ func TestParseStorageEndpoints(t *testing.T) {
 		expectedErr     error
 	}{
 		{"", "http://localhost/export", nil},
-		{"testhost", "http://localhost/export", errInvalidArgument},
-		{"", "http://localhost:9000/export", errInvalidArgument},
+		{
+			"testhost",
+			"http://localhost/export",
+			errors.New("Invalid Argument localhost, port mandatory when --address <host>:<port> is used"),
+		},
+		{
+			"",
+			"http://localhost:9000/export",
+			errors.New("Invalid Argument localhost:9000, port configurable using --address :<port>"),
+		},
 		{"testhost", "http://localhost:9000/export", nil},
 	}
 	for i, test := range testCases {
 		globalMinioHost = test.globalMinioHost
 		_, err := parseStorageEndpoints([]string{test.host})
-		if err != test.expectedErr {
-			t.Errorf("Test %d : got %v, expected %v", i+1, err, test.expectedErr)
+		if err != nil {
+			if err.Error() != test.expectedErr.Error() {
+				t.Errorf("Test %d : got %v, expected %v", i+1, err, test.expectedErr)
+			}
 		}
 	}
 	// Should be reset back to "" so that we don't affect other tests.