Remove mscorlib.ni.dll before running tests

The test layout folder that is created when we run tests includes an
mscorlib native image. This native image is specific to windows (since
we use the windows version of the runtime when building a test layout,
even when building a test layout for Linux or OSX) and the runtime
will not boot if it is present.

When we run tests from CI, we instruct Jenkins to not copy native
images, but if you are running tests by hand you need to either make
sure you don't copy native images over or remove them before running
tests.

With more folks wanting to use run-test.sh by hand, we should just
make run-test.sh responsible for cleaning up these native images.

Fixes #2605

Author: ellismg

run-test.sh

@@ -190,9 +190,17 @@ runtest()
 
   copy_test_overlay $dirName
 
+  pushd $dirName > /dev/null
+
+  # Remove the mscorlib native image, since our current test layout build process
+  # uses a windows runtime and so we include the windows native image for mscorlib
+  if [ -e mscorlib.ni.dll ]
+  then
+    rm mscorlib.ni.dll
+  fi
+  
   # Invoke xunit
 
-  pushd $dirName > /dev/null
   echo
   echo "Running tests in $dirName"
   echo "./corerun xunit.console.netcore.exe $testDllName -xml testResults.xml -notrait category=failing -notrait category=OuterLoop -notrait category=$xunitOSCategory"