Change the Protocol output capture to use the stdout buffer instead of the print redefinition function

**[Original report](https://bitbucket.org/fchampalimaud/pybpod-gui-plugin/issue/8) by Ricardo Jorge Vieira Ribeiro (Bitbucket: [UmSenhorQualquer](https://bitbucket.org/UmSenhorQualquer), GitHub: [UmSenhorQualquer](https://github.com/UmSenhorQualquer)).**

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check class bpod_runner
