Lower PLOG(ERROR) to PLOG(WARNING) if unable to find realpath

We were emitting a PLOG(ERROR) from class_loader_context if we are
unable to find the dex-files realpath. This is an issue because
InMemoryDexClassLoader and some --redefine-stress tests cause this
message to be printed, making the test fail.

This also brings it more into line with other logs in this file.

Test: ./test/run-test --host --jvmti-redefine-stress 071
Change-Id: Idc21bf89be02ca9263fbec7f28fdf036196ab58c
diff --git a/runtime/class_loader_context.cc b/runtime/class_loader_context.cc
index 3bd4596..2282da0 100644
--- a/runtime/class_loader_context.cc
+++ b/runtime/class_loader_context.cc
@@ -220,7 +220,7 @@
         // If we can't get the realpath of the location there might be something wrong with the
         // classpath (maybe the file was deleted).
         // Do not continue in this case and return false.
-        PLOG(ERROR) << "Could not get the realpath of dex location " << raw_location;
+        PLOG(WARNING) << "Could not get the realpath of dex location " << raw_location;
         return false;
       }