Revert "Merge pull request #8942 from yahonda/tested_only_with_mysql"

This reverts commit 1fc294f988e93ac59057a16b0e44b9cf93af9720, reversing
changes made to fb9ac47c286fbdfe05263d4d0346e50892090603.

Reason: these tests should run fine independent of database, since they
should only take into account the configuration options. The problem was
related to a change in the way "nil" is handled by the rescue clause, in
Ruby 2.0 it raises an exception asking for class or module, in 1.9 it
passes.
Improve mysql database tasks handling to ensure we always rescue from an exception

We were previously rescuing "nil" when no exception class was found.
This does work in 1.9.3, but does not in 2.0, raising an exception
asking for a class or module to be given to the rescue clause.

Thanks @yahonda for catching this.