Correct faulty Chef search query

The search returns a Hash, not a list, so we need
to remove the reference to [0] in the memcached_servers
library routine call otherwise you get:

undefined method `[]' for nil:NilClass

in chef-client runs.

Change-Id: I479aca833a2eb80fa2baf3e54809b2edaa713b89
Merge "Correct faulty Chef search query"