[python] fix tests, tornado ssl fix

[tomplus]

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Description of the PR

Fixes related to:

1. Travis doesn't know that tests fail because an exit codes from bash scripts are always zero - fixed
2. Tornado client doesn't work in python < 2.7.9 - fixed
3. Some tests are skipped because public PetStore endpoint has incorrect data. Travis use local instance of PetStore server and all test can run. I removed @skip and also force endpoint name to localhost. IMO it'll remind developers about starting a local instance. Test endpoint returns invalid data #6907

Please take a look: @wing328 @taxpon @frol @mbohlool @cbornet @kenjones-cisco

[frol]

Travis doesn't know that tests fail because an exit codes from bash scripts are always zero - fixed

Does this mean that flake8 failure will be also ignored? Should we use set -e or run the scripts with explicit bash -e ./test_python2_and_3.sh?

[tomplus]

Travis sees an exit code from a script but it's exit code from last command. So we have situation where python test failed but flake8 "covers" it and returns 0. Now I exit immediately if python tests failed. flake8 is a last command so its code will be interpreted correctly. If flake return non-zero code, Travis will notice it.

I consider using set -e but I think it would be too big change in this quite simple case.

[tomplus]

Tornado client doesn't work in python < 2.7.9 - fixed

Finally I had to drop compatibility with older Python. It's more complicated and I'll fix it in next PR.

[frol]

Looks good to me!

[wing328]

cc @toumorokoshi as well