Make GetErrorName allocate the output buffer.

Previously we were simply returning a static pointer which isn't
allowed by the spec.

Test: mma -j40 test-art-host
Change-Id: I84cfb81e58d479c7c0d5ee352f5b005183895c82
diff --git a/test/907-get-loaded-classes/get_loaded_classes.cc b/test/907-get-loaded-classes/get_loaded_classes.cc
index afbb774..36d33b6 100644
--- a/test/907-get-loaded-classes/get_loaded_classes.cc
+++ b/test/907-get-loaded-classes/get_loaded_classes.cc
@@ -48,6 +48,7 @@
     char* err;
     jvmti_env->GetErrorName(result, &err);
     printf("Failure running GetLoadedClasses: %s\n", err);
+    jvmti_env->Deallocate(reinterpret_cast<unsigned char*>(err));
     return nullptr;
   }