Use regex to fill in config-sample. Prevents translators from needing to...

Use regex to fill in config-sample. Prevents translators from needing to manually translate 'database_name_here' (and friends). see #18180.

git-svn-id: https://core.svn.wordpress.org/trunk@19701 1a063a9b-81f0-0310-95a4-ce76da25c4cd