test: move basic mesh test under './setup.py test'

In short: this commit moves the basic MeshConnection test cases to the
`./setup.py test` test suites (which are located in the unit/ now) and
removes the test-run submodule, which is not needed anymore.

A bit background: we have a testing framework called test-run, whose
primary goal is to give ability to manage tarantool instances from a
test. Historically tarantool-python does not use test-run for testing
(it uses several simple python helpers instead), but a test-run based
test was added in the scope of #106. The idea was to reuse test-run code
more and eventually port other tests to test-run.

The objective reality reveals several problems in the idea, which looked
nice in theory.

The main problem is the cyclic dependency between test-run and
tarantool-python submodules. It consumes an extra time at recursive git
clone and places old submodule revisions in a deeply nested level. The
latter may confuse linter tools, which search for files recursively (see
[1]).

Other problems look solvable, but I'll list them, because they give
considerable weight in my impression that we should get rid of the
test-run submodule within this repository:

1. test-run based tests were not run in CI and may break silently so
   (it already occurs once).
2. The first bullet looks easy to fix, but it is unclear whether it is
   right to depend on a submodule in the `./setup.py test` testing or we
   should keep only built-in and packaged testing tools in the
   dependencies.
3. Porting tests to test-run may require extra effort and nobody was
   eager to pay time for that.
4. Existing tooling for managing tarantool instances is enough for
   testing of the connector and, at the same time, it is quite simple.
   So if we'll meet a problem, it is easier to fix.
5. test-run supports only Python 2 at the moment (however it'll be fixed
   soon, see [2]).

To sum up, the experiment with the test-run submodule looks unsuccessful
and I think we should stop it for now. If we'll decide to try again, we
should consider all described problems and implement everything in a way
that does not hurt us.

[1]: tarantool/test-run#266 (comment)
[2]: tarantool/test-run#20

Fixes #111

Author: Totktonada

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "test-run"]
-	path = test-run
-	url = https://github.com/tarantool/test-run

Makefile

@@ -1,7 +1,6 @@
 .PHONY: test
 test:
 	python setup.py test
-	cd test && ./test-run.py
 coverage:
 	python -m coverage run -p --source=. setup.py test
 cov-html: