[android-toolchain] Fix the location of the android tools

The current directory structure for the android sdk does NOT
match the one that google creates. The tools are not in a
tools subdirectory when they should be. As a result things like
the sdkmanager do not run. It also causes problems for Xamarin Studio
since its looking for things in different places.

This commit fixes up the DestDir metadata to make sure the tools
are extacted to the correct directory.

build-tools/android-toolchain/android-toolchain.projitems

@@ -31,6 +31,7 @@
     </AndroidSdkItem>
     <AndroidSdkItem Include="tools_r24.4.1-macosx.zip">
       <HostOS>Darwin</HostOS>
+      <DestDir>tools</DestDir>
     </AndroidSdkItem>
     <AndroidSdkItem Include="platform-N_r01.zip">
       <HostOS></HostOS>