2.9.0

Changelog:

Benedikt Heine:
Do not display the password variables in log
Remove instantiation of void icinga2 database
Reorder setup scripts and run them with run-parts
Move custom_run into separate file
Release announcements in icingaweb2 and on console
Add warning about old mounted php5 sessions folder
Map all boolean values to 0 or 1
Fix whitespace indentation
Add helpers file
Allow concatenation of evaluate_boolean
Sleep until MySQL server is online
remove unused DIRECTOR_API_PASSWORD
Put icingaweb2 modules into independent layer
Add docker-compose.override.yml to gitignore
Fix variable name typo
Fix typos
Make init scripts able to have external MySQL
Grant all rights to MySQL user
Remove (IDO|ICINGAWEB2|DIRECTOR)_PASSWORD
Add support for docker official mariaDB image
Move data into separate data directory
Fail fast in setup scripts
Use env file for MySQL secrets
Add notification about bundled MySQL deprecation
Do not mount certificates read only
Expose ports in docker-compose project
Do not fail when removing modules for safety
Rename graphite web_url to url
Parametrized locale generation
Add docs for API
Allow MYSQL_ROOT_PASSWORD to be empty
Install icingaweb2 modules via apt
Remove superfluous export directive
Indent run commands to be in line with first argument
Sort package arguments

Christian Uhlmann:
add libdbd-mysql-perl

Jordan Jethwa:
Add dnsutils
Start icinga2 in foreground
temporary fix as check_run not run starting in foreground

Michaël Zasso:
fix certificate check in setup

Thomas Widhalm:
change pulling icinga key from wget to curl
upgrade Icinga packages URL to the new tld remove -k from curl