Make missing public soname error message clear.

If a public library is missing, make it clear that there is no
library with that soname that is missing. This can help diagnose
problems if a library exists, but the library doesn't have the right
soname.

Bug: 29400363
(cherry picked from commit 9a84d90c753dd934c3086322f6ba6b7a1f580c8c)

Change-Id: Ie2306a2e28aff779d07441dc8af078256b184f8a
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 9eb3a65..e2d57f0 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -2403,8 +2403,8 @@
     find_loaded_library_by_soname(&g_default_namespace, soname.c_str(), &candidate);
 
     if (candidate == nullptr) {
-      DL_ERR("error initializing public namespace: \"%s\" was not found"
-             " in the default namespace", soname.c_str());
+      DL_ERR("error initializing public namespace: a library with soname \"%s\""
+             " was not found in the default namespace", soname.c_str());
       return false;
     }