Remove test_ prefix from methods called by other tests

Methods test_retrieve_single and test_retrieve_single_by_device got
called from other methods. In case any of the caller functions fail when
calling any of these two functions, the callee is shown as failing. This
hides what test actually failed.

This change renames the callees so that the callers are shown when they
fail.

Issue: HIC-98
Change-Id: Ia61afbcb53f3fe46c9545538a52d197f6db90461
1 file changed