HG Test: Tests may erroneously pass: error checking needs improvement

[gnuoyd]

This came up while debugging the UCX plugin for NA. The "lookup" test run by hg_test_rpc:hg_test_rpc_lookup() called hg_request_wait(request, HG_MAX_IDLE_TIME, NULL), which timed out after HG_MAX_IDLE_TIME milliseconds (30 seconds) because no progress was made. Since hg_test_rpc_lookup() did not check for an error return from hg_request_wait(), it continued with the next test step. In this way, the test took several minutes to complete, but it still passed.