use native libs bundled with jna when running tests

Summary:
This fixes test_ng test for appveyor.
The default logic of jna is to load native libs installed in the system
(http://java-native-access.github.io/jna/4.4.0/javadoc/overview-summary.html).
It may be the case that the system has jna native lib incompatible with what we use
(discussion: #1364) - and nailgun will not be able to start.

Test Plan:
Tested on appveyor: https://ci.appveyor.com/project/ilya-klyuchnikov/buck-07nvh/build/6
Tested on travis: https://travis-ci.org/ilya-klyuchnikov/nailgun/builds/238824664

Reviewed By: Coneko

fbshipit-source-id: 5e7c8f8

third-party/nailgun/pynailgun/test_ng.py

@@ -83,7 +83,7 @@ def preexec_fn():
             creationflags = DETACHED_PROCESS
 
         self.ng_server_process = subprocess.Popen(
-            ['java', '-jar', self.getNailgunUberJar(), self.transport_address],
+            ['java', '-Djna.nosys=true', '-jar', self.getNailgunUberJar(), self.transport_address],
             close_fds=True,
             preexec_fn=preexec_fn,
             creationflags=creationflags,