Bug: Fix order of 'arakoon_multi_get' result

The 'multi_get' operation yields a 'string array' instead of a
'string list', which has a reverse ordering. This commit fixes this
oversight in the client call result decoding code, and hardens the
related testcase.

Change-Id: I0dc6bf658d96568e2e04c758c1b1919401d0c223
Fixes: ARAKOON-436
See: http://jira.incubaid.com/browse/ARAKOON-436