[ticket/10966] Introduce MySQL base class

PHPBB3-10966
Merge remote-tracking branch 'nickvergessen/ticket/10966' into develop

* nickvergessen/ticket/10966:
  [ticket/10966] Introduce MySQL base class
[ticket/11501] Assert the variables instead of fail() with the condition

PHPBB3-11501
[ticket/11501] Remove test_ prefix from data provider methods

PHPBB3-11501
Merge remote-tracking branch 'nickvergessen/ticket/11501' into develop

* nickvergessen/ticket/11501:
  [ticket/11501] Remove test_ prefix from data provider methods
  [ticket/11501] Assert the variables instead of fail() with the condition