Rex::Test::Base::run_task doesn't allow to pass arguments to tasks

In tests one often ends up with a construct along the lines of:

my $t = Rex::Test::Base->new;
$t->name('explodey_test');
$t->run_task('ACMECorp:Server:setup');

Some tasks may need some extra arguments to do something useful, e.g. useradd needing the user name. Naively one would try something like:

$t->run_task('ACMECorp:Useradd', username => 'Frank');

But due to restrictions in the code no arguments can be passed, which makes tests a lot more tedious.

Start by locating Rex::Test::Base::run_task and inspect how it currently handles task arguments. Trace the existing test-task setup, then add coverage showing that arguments such as a username can be passed and used by a task; done means the example invocation works without making tests more tedious.