Move System.Net tests back to pre-release versions temporarily to fix missing SecureString

The stable versioned packages use an older codebase currently than the latest pre-release.
That codebase is still using SecureString in System.Private.Networking, but the dependency
was omitted since crypto is still pre-release but networking had to be marked stable for UWP.
This missing dependency was causing tests to fail.

Rather than just list the dependency I am moving these tests back to pre-release packages
for the System.Net contracts, since System.Net packages are under active development
it is better to have the tests running against latest than the stable bits.

Once we have newer versions published we'll update these tests to use those.

Author: ericstj

src/System.Net.Http.WinHttpHandler/tests/FunctionalTests/project.json

@@ -4,8 +4,8 @@
     "System.Globalization": "4.0.10",
     "System.IO": "4.0.10",
     "System.IO.Compression": "4.0.0",
-    "System.Net.Http": "4.0.0",
-    "System.Net.Primitives": "4.0.10",
+    "System.Net.Http": "4.0.0-beta-*",
+    "System.Net.Primitives": "4.0.10-beta-*",
     "System.Resources.ResourceManager": "4.0.0",
     "System.Runtime.Extensions": "4.0.10",
     "System.Runtime.Handles": "4.0.0",

src/System.Net.Http.WinHttpHandler/tests/FunctionalTests/project.lock.json

@@ -3,8 +3,8 @@
     "Microsoft.Win32.Primitives": "4.0.0",
     "System.Globalization": "4.0.10",
     "System.IO": "4.0.10",
-    "System.Net.Http": "4.0.0",
-    "System.Net.Primitives": "4.0.10",
+    "System.Net.Http": "4.0.0-beta-*",
+    "System.Net.Primitives": "4.0.10-beta-*",
     "System.Resources.ResourceManager": "4.0.0",
     "System.Runtime.Extensions": "4.0.10",
     "System.Runtime.Handles": "4.0.0",