With previous algorithm, work was given to additional test nodes only when:
- we were previously below the needed capacity
- when another test node was dying

Now, as soon as a new test node is added, we move work of overloaded test nodes to
idle test nodes. We try to move only test suite using many test nodes to avoid having to
wait for building time.

This allows to have better distribution of the work with the idea to have more quickly test results.
This will avoid cases where we have several testnodes assigned to no work at all.

Finally, fixed distribution algorithm to avoid some unfair cases where a test suite might
have more test node than another while they both ask for the same number of test nodes.