MEN-1405: release_tool: Auto-provide next version needed for a release.
MEN-1405: release_tool: Auto-provide next version needed for a release.

It can't be fully automatic, but offers the user a log, and he can
decide whether a new release of the service is necessary.

Changelog: none

Signed-off-by: Kristian Amlie <505e66ae45028a0596c853559221f0b72c1cee21@northern.tech>

pasinskim/integration,pasinskim/integration,pasinskim/integration