Add xUnit test runner script

Unfortunately a wrapper is needed because `LD_LIBRARY_PATH` must be set
to avoid having to place build artifacts (specifically
`libpsl-native.so`) out-of-tree to run tests.

xunit.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+
+# Build native components
+pushd src/libpsl-native
+cmake -DCMAKE_BUILD_TYPE=Debug .
+make -j
+ctest -V
+## Work-around dotnet/cli#710
+export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$(pwd)/src"
+popd
+
+# Run xUnit tests
+pushd test/csharp
+## Build
+dotnet build
+## Work-around dotnet/cli#753
+cp -r ../../src/Microsoft.PowerShell.Linux.Host/{Modules,*ps1xml} bin/Debug/dnxcore50/
+## Test
+dotnet test
+popd