Look for JDK 1.8 before JDK 1.6 (#1)

Fixes: https://bugzilla.xamarin.com/show_bug.cgi?id=52928

The order of the default JDK search was incorrect. We should be searching
for the latest JDK first since this is what the google tooling needs.

This commit switches the order in which we do the search.

Author: dellis1972

src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkWindows.cs

@@ -114,14 +114,14 @@ protected override string GetJavaSdkPath ()
 					Logger (TraceLevel.Info, $"  Key {key_name} found.");
 
 					// No matter what the CurrentVersion is, look for 1.6 or 1.7 or 1.8
-					if (CheckRegistryKeyForExecutable (RegistryEx.LocalMachine, subkey + "\\" + "1.6", "JavaHome", wow64, "bin", JarSigner))
-						return RegistryEx.GetValueString (RegistryEx.LocalMachine, subkey + "\\" + "1.6", "JavaHome", wow64);
+					if (CheckRegistryKeyForExecutable (RegistryEx.LocalMachine, subkey + "\\" + "1.8", "JavaHome", wow64, "bin", JarSigner))
+						return RegistryEx.GetValueString (RegistryEx.LocalMachine, subkey + "\\" + "1.8", "JavaHome", wow64);
 
 					if (CheckRegistryKeyForExecutable (RegistryEx.LocalMachine, subkey + "\\" + "1.7", "JavaHome", wow64, "bin", JarSigner))
 						return RegistryEx.GetValueString (RegistryEx.LocalMachine, subkey + "\\" + "1.7", "JavaHome", wow64);
 
-					if (CheckRegistryKeyForExecutable (RegistryEx.LocalMachine, subkey + "\\" + "1.8", "JavaHome", wow64, "bin", JarSigner))
-						return RegistryEx.GetValueString (RegistryEx.LocalMachine, subkey + "\\" + "1.8", "JavaHome", wow64);
+					if (CheckRegistryKeyForExecutable (RegistryEx.LocalMachine, subkey + "\\" + "1.6", "JavaHome", wow64, "bin", JarSigner))
+						return RegistryEx.GetValueString (RegistryEx.LocalMachine, subkey + "\\" + "1.6", "JavaHome", wow64);
 				}
 
 				Logger (TraceLevel.Info, $"  Key {key_name} not found.");