security: Construct KeyChain from configuration file.

Change-Id: Iaddac24e2c4e199fdde83fa1d0067a87e18729c4
Refs: #1532
diff --git a/src/util/config-file.cpp b/src/util/config-file.cpp
index 162cf60..6ba45aa 100644
--- a/src/util/config-file.cpp
+++ b/src/util/config-file.cpp
@@ -40,9 +40,21 @@
 {
   using namespace boost::filesystem;
 
-  path home(std::getenv("HOME"));
-  if (!home.empty())
+#ifdef NDN_CXX_HAVE_TESTS
+  if (std::getenv("TEST_HOME"))
     {
+      path testHome(std::getenv("TEST_HOME"));
+      testHome /= ".ndn/client.conf";
+      if (exists(testHome))
+        {
+          return absolute(testHome);
+        }
+    }
+#endif // NDN_CXX_HAVE_TESTS
+
+  if (std::getenv("HOME"))
+    {
+      path home(std::getenv("HOME"));
       home /= ".ndn/client.conf";
       if (exists(home))
         {