Fix Usage of ets:lookup_element()
Fix Usage of ets:lookup_element()

ets:lookup_element() throws error:badarg exception if the element
being looked up doesn't exist. This change set wraps the calls to
lookup_element() in a try-catch block and returns an empty list if an
element isn't found.

Change-Id: I5578f044689d652c36285d989bd8d048b0f86f16
Reviewed-on: http://review.couchbase.org/10460
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

membase/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,daverigby/ns_server,membase/ns_server,membase/ns_server,nimishzynga/ns_server,ceejatec/ns_server,membase/ns_server,vzasade/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,vzasade/ns_server,mschoch/ns_server,nimishzynga/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,nimishzynga/ns_server,vzasade/ns_server,membase/ns_server,mschoch/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,vzasade/ns_server,membase/ns_server,daverigby/ns_server,mschoch/ns_server,daverigby/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,nimishzynga/ns_server,daverigby/ns_server