Add Console_TEST.cc test that ensures we are getting output

**Original report ([archived issue](https://osrf-migration.github.io/sdformat-gh-pages/#!/osrf/sdformat/issues/162)) by clalancette (Bitbucket: [clalancette](https://bitbucket.org/%7B02b311e1-297d-4232-89c4-5485d0a02911%7D/), GitHub: [clalancette](https://github.com/clalancette)).**

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@chapulina pointed out that gazebo has a test ensuring that the console is actually printing what we expect, when we expect it. It does this by writing the output to a file, then checking that the file is what we expect. It is implemented here:

https://bitbucket.org/osrf/gazebo/src/45f77842932c95d747d2f20df98aed613792b295/gazebo/common/Console_TEST.cc?fileviewer=file-view-default

https://bitbucket.org/osrf/gazebo/src/45f77842932c95d747d2f20df98aed613792b295/test/util.hh?fileviewer=file-view-default#util.hh-66

We should do a similar thing in sdformat.

Use the linked Gazebo Console_TEST.cc and test/util.hh as reference implementations, then locate sdformat's console output entry points and existing test layout. Add an analogous Console_TEST.cc test that captures console output and verifies the expected contents, using the project's normal test command to confirm it passes.

Written by the indexing model from the issue text.