Requirement versions were set in the first place to limit the
buginess. However, after some time it appears that it made more
harm than good, as discussed in:
https://review.openstack.org/#/c/388003/
In this commit we remove the versions for all the requirements.
In the future, if a specific dependency version if causing some issue
we should reintroduce the version for this dependency to block the
unstable version.
Sem-Ver: bugfix
Change-Id: Ia42509bf2bf9012cc03c8bb25b84f465425e2aad
e1ed6abec2