[cookbook][doctrine/reverse_engineering] fixed extension prefix for mapping file generated by doctrine:mapping:convert
[cookbook][doctrine/reverse_engineering] fixed output path specification for yml or xml mapping file
[cookbook][doctrine/reverse_engineering] add description to insert namespace
[cookbook][doctrine/reverse_engineering]changed the second command to execute from doctrine:mapping:import to doctrine:mapping:convert
Merge pull request #2578 from 77web/fix-reverse_engineering-doc

[cookbook][doctrine] fixed reverse_engineering doc