[api tests][pyresttest] test tags_api get_discussions_by_blog fail

1. on directory tests create 'build' folder
2. cd tests/build
3. cmake -DTEST_NODE=<address_of_your_hivemind> .. (example: cmake -DTEST_NODE=http://127.0.0.1:8080 ..)
4. uncommet test in file: tests_api/hivemind/pyrest_tests/5000000/tags_api/tags_api_test.yaml :

#  - test:
#    - name: "get_discussions_by_blog"
#    - variable_binds:
#      - method: "get_discussions_by_blog"
#      - args: '{"tag":"steemit","limit":1}'
#    - <<: *base_test

5. run in console 'ctest -R api/pyresttests/5000000/tags_api --output-on-failure'