[ticket/13181] Replace database credentials with placeholders in sphinx conf

PHPBB3-13181
Merge pull request #3042 from naderman/ticket/13181

[ticket/13181] Replace database credentials with placeholders in sphinx conf
Merge branch 'develop-ascraeus' into develop

# By Nils Adermann
# Via Dhruv Goel (1) and Nils Adermann (1)
* develop-ascraeus:
  [ticket/13181] Replace database credentials with placeholders in sphinx conf