shill: Use an empty environment for NSS cert lookup.

This ensures that the nss-get-cert script will use the correct NSS database
location.

BUG=chromium-os:29511
TEST=unit tests, tested on device that NSS lookup succeeds when running shill
with incorrect HOME

Change-Id: I246a65ba53d0476332e3a458680b114f8ea5a4e5
Reviewed-on: https://gerrit.chromium.org/gerrit/20368
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/nss_unittest.cc b/nss_unittest.cc
index 57163f7..1bfb4ba 100644
--- a/nss_unittest.cc
+++ b/nss_unittest.cc
@@ -10,6 +10,7 @@
 
 using std::vector;
 using testing::_;
+using testing::NotNull;
 using testing::Return;
 using testing::SetArgumentPointee;
 
@@ -46,7 +47,8 @@
 
 TEST_F(NSSTest, GetCertfile) {
   EXPECT_CALL(glib_,
-              SpawnSync(_, GetCertfileArgv("pem"), _, _, _, _, _, _, _, _))
+              SpawnSync(_,
+                        GetCertfileArgv("pem"), NotNull(), _, _, _, _, _, _, _))
       .WillOnce(Return(false))
       .WillOnce(DoAll(SetArgumentPointee<8>(1), Return(true)))
       .WillOnce(DoAll(SetArgumentPointee<8>(0), Return(true)));