evolve: add logic to continue interrupted content-divergence resolution
We continue the interrupted content-divergence using the logic to complete
content-divergence which we refactored in it's own function few patches ago.
We had to delete evolvestate file before using cmdutil.amend() because otherwise
we can't use the function. This leads to a hack which deletes the evolvestate
file, we may want to not to use the high level API function here. Also we had to
pass evolvestate also to _completecontentdivergent function because of this.
This patch also, adds a test which demonstrates that the logic works fine.
