[#2102] Update release tasks.

Problem
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After updating buildbot , the release build system was broken.


Changes
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Update release relates task to match the new buildbot.

At first I wanted to move all release related code into server/pavement.py ... but then we also have a release process for client and webadmin... .. so we need to keep this shared code.

Documentation was updated 
https://trac.chevah.com:10443/wiki/Development/ProductRelease

release on staging will just run test and publish doc and kits.

release on production will run test, publish and will also do a merge in master... in the future I plan to udpate the code so that it will also create the tag.

This means that release branch is not landed with PQM but with RQM. Please check that documentation is clear about that... if not please update the documentation to make it obvious.


How to test
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reviewers: @alibotean @lgheorghiu 
You can test the release on staging... but not the release in production.

I have already released server 2.4.0 with this code and it should be fine.

This is just to let you know about the changes.
Thanks