Refactor rename collection tests

Currently we have some tests in jstests/core named "rename{0-8}.js", this cause some confusion since some of them test the renameCollection command and some other the $rename operator. Moreover some of these test are very small and can be grouped together.

Tasks that will be executed under this ticket:

• Remove the require_fastcount tag by using countDocuments instead.
• Split rename.js in rename_collection.js and rename_collection_capped.js.
• Merge rename2.js in rename_collection.js.
• Merge rename3.js in rename_collection.js.
• Rename rename4.js into rename_operator.js.
• Rename rename5.js into rename_operator_missing_source.js.
• Rename rename6.js into rename_collection_long_name.js.
• Rename rename7.js into rename_collection_different_dbs.js
• Rename rename8.js into rename_collection_system_db.js
• Rename rename_stayTemp.js into rename_collection_staytemp.js
• Blacklist tests by tags instead of explicit blacklisting