scenario_test/README: Remove redundant brake tag
scenario_test/README: Remove redundant brake tag

Also adds the language type of code blocks.

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>

Dipsingh/gobgp,j-kato/gobgp,a16/gobgp,fujita/gobgp,tamihiro/gobgp,ishidawataru/gobgp,osrg/gobgp,a16/gobgp,tamihiro/gobgp,a16/gobgp,a16/gobgp,ishidawataru/gobgp,a16/gobgp,fujita/gobgp,a16/gobgp,tamihiro/gobgp,fujita/gobgp,ishidawataru/gobgp,osrg/gobgp,osrg/gobgp,fujita/gobgp,a16/gobgp,j-kato/gobgp,tamihiro/gobgp,Dipsingh/gobgp,Dipsingh/gobgp,j-kato/gobgp,osrg/gobgp