Respect caller DT_RUNPATH in dlopen().

When dlopen-ing a library, add the caller's DT_RUNPATH to the directory search
list. This fixes dlfcn.dt_runpath in bionic-unit-tests-glibc(32|64).

Bug: 21899363
Change-Id: Ife6a7e192939292cf4dc291b7e6b95945761cde3
diff --git a/tests/dlfcn_test.cpp b/tests/dlfcn_test.cpp
index 92e3287..00cbdc6 100644
--- a/tests/dlfcn_test.cpp
+++ b/tests/dlfcn_test.cpp
@@ -1072,7 +1072,7 @@
   ASSERT_TRUE(fn != nullptr) << dlerror();
 
   void *p = fn();
-  ASSERT_TRUE(p == nullptr);
+  ASSERT_TRUE(p != nullptr);
 
   dlclose(handle);
 }