test: update test-run

The following commits are land into the submodule with this update:

- 96dea99 Enable luacheck on Travis CI
- daff045 Add luacheck config and fix warnings found by luacheck

Most of the changes are about test-run's Makefile and CI, but there is
one change in the testing framework itself:

 | diff --git a/test_run.lua b/test_run.lua
 | index 2a8d713..06fbf6c 100644
 | --- a/test_run.lua
 | +++ b/test_run.lua
 | @@ -163,7 +163,6 @@ local function wait_fullmesh(self, servers)
 |                  log.info("%s: bootstrapped", server)
 |                  break
 |              end
 | -            local info = self:eval(server, "box.info")
 |              fiber.sleep(0.01)
 |          end
 |          -- wait all for full mesh

This change removes the call, whose result is not used. On the first
glance, it should not change any behaviour. However `test_run:eval()`
performs a network request and it is good to get rid of it.

The change is tiny and should not affect anything in tarantool testing,
but I decided to commit it separately from others to don't hide anything
and ease bisect if we'll observe any positive or negative impact. IOW,
just in case.