fix domconf merge

[rayderua]

here is a problem with merging nested hashes using +: they are not merged deeply.

Example:

$h1 = {  'a' => {  'x' => 1,  'y' => 2  },  'b' => 1 }
$h2 = {  'a' => {  'y' => 99 } }
$h3 = $h1 + $h2
'''
Result:

{ a => { y => 99 }, b => 1 }

As a result, we cannot correctly merge the domain domconf with the profile domconf.
The solution is to use deep_merge() instead.