[build] use JDK 8 if JDK 9 is installed

Context: dotnet/java-interop#226

At the current time, we will not be able to use JDK 9 for Android. Some
of our build agents (VSTS), now have JDK 9 installed, so we need to
make a few changes to make sure JDK 8 is picked up instead.

Changes:
- Bump to java.interop/master/55c56f7
- Calls to `make -C external/Java.Interop` need to pass `JI_MAX_JDK=8`

Author: jonathanpeppers

Makefile

@@ -90,8 +90,8 @@ prepare-external:
 	nuget restore Xamarin.Android-Tests.sln
 	$(foreach conf, $(CONFIGURATIONS), \
 		(cd external/xamarin-android-tools && make prepare CONFIGURATION=$(conf)) && \
-		(cd $(call GetPath,JavaInterop) && make prepare CONFIGURATION=$(conf)) && \
-		(cd $(call GetPath,JavaInterop) && make bin/Build$(conf)/JdkInfo.props CONFIGURATION=$(conf)) && ) \
+		(cd $(call GetPath,JavaInterop) && make prepare CONFIGURATION=$(conf) JI_MAX_JDK=8) && \
+		(cd $(call GetPath,JavaInterop) && make bin/Build$(conf)/JdkInfo.props CONFIGURATION=$(conf) JI_MAX_JDK=8) && ) \
 	true
 
 prepare-deps: prepare-external

build-tools/scripts/RunTests.targets

@@ -45,7 +45,7 @@
   <Target Name="RunJavaInteropTests">
     <MSBuild Projects="$(JavaInteropSourceDirectory)\Java.Interop.sln" Condition=" '$(HostOS)' == 'Windows' " />
     <Exec
-        Command ="make -C &quot;$(JavaInteropSourceDirectory)&quot; CONFIGURATION=$(Configuration) all"
+        Command ="make -C &quot;$(JavaInteropSourceDirectory)&quot; CONFIGURATION=$(Configuration) all JI_MAX_JDK=8"
         Condition=" '$(HostOS)' != 'Windows' "
     />
     <SetEnvironmentVariable Name="ANDROID_SDK_PATH" Value="$(AndroidSdkFullPath)" />