[VOL-2991] Remove incorrect locks from backend.go

This commit consists of the following:

1) Remove the locks in the backend.go that were forcing all
ETCD requests to be serialized.

2) Minor change to the log to check whether a log level is
set before outputting message with serialized content.

Change-Id: I093eae006d9090fbeec75916ad82c329f1c61723
2 files changed