test: update test-run

Run a unit test from a var directory. It is needed to, say, allow a test
to write a log file to a gitignored directory.

The only behaviour change observed on tarantool's tests is that
unit/swim.test and unit/swim_proto.test write a log.txt file to a test
var directory ./test/xxx_unit instead of ./test.

test-run @ 1aeb35b4

-Subproject commit 59bae401fe7ef9dbb3d958a6c5d9c0a97746ed82
+Subproject commit 1aeb35b41024d7dc0ac4db8d998a473d213f2755