evolve: prompt user to select destination for stabilization in case of split This patch adds functionality to prompt user to select a revision when there exists multiple stabilization destination because of split on multiple branches. Test are also added for the feature. I am not sure whether this is the best message which we can show, if people have suggestions I will like to improve the messages shown in prompt.

tests: remove some tests which are moved to dedicated files The tests in test-unstable.t files are now moved to their dedicated file with all the cases to that in that file. Let's delete them from here.