test: use Python 3

Python 2 support is EOL [1] and we should support to run our python
tests using Python 3.x. test-run used as test-runner for memcached
already supports Python 3, see [2].

Patch enable running tests using Python 3 on CI and removes
test/var/memcached symlink.

1. https://www.python.org/doc/sunset-python-2/
2. tarantool/test-run#20

Closes #82

Author: ligurio

.github/workflows/testing.yaml

@@ -33,10 +33,10 @@ jobs:
 
       - run: cmake .
 
-      - name: Setup Python 2 for tests
+      - name: Setup Python 3 for tests
         uses: actions/setup-python@v2
         with:
-          python-version: 2.7
+          python-version: 3.7
 
       - name: Install test requirements
         run: pip install -r test-run/requirements.txt

README.md

@@ -15,10 +15,9 @@ Memcached protocol 'wrapper' for Tarantool.
 
  * Tarantol 1.6.8+ with header files (tarantool && tarantool-dev packages).
  * Cyrus SASL library (with header files)
- * Python >= 2.7, <3 with next packages (for testing only):
-   - PyYAML
-   - msgpack-python
-   - six==1.9.0
+ * Python >= 3.7 with next packages (for testing only):
+   - PyYAML 5+
+   - gevent 21+
 
 ### Installation