Test for FF'ability is left to catching a fail from git plugin

[RandomSort]

In GitIntegrationStrategy line 130 -> 139 we try to do a fastforward merge catching errors.
We do not care or trigger on whether the merge failed or if it was not possible to fastforward merge.

This does not seem to be the best strategy. We can test whether the merge can possibly be a FF merge before even attempting it by for instance checking the output of git log master..ready/mydelivery if this is empty a ff merge is possible.

This is of course neither blocking or critical, just a refactoring.