[#1273] Fix compat OS administration for Domain Controller.

Problem description
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The tests should run also on build slaves that are integrated in Active Directory.

Changes description
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The buildbot under the build slave that is integrated in the Active Directory must run as domain administrator in order to have permissions to create the testing accounts.
The 'CHEVAH' domain was created having the primary domain controller named 'CHEVAH-DC'.
Most of the functions from OS administration must have an additional argument 'server' which points to the primary domain controller if the computer is integrated in the domain. If the test must run using local computer account the 'server' argument is None.

How to try and test the changes
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reviewers @adiroiban @alibotean

Look at the code and run the tests on all current build slaves and compat-win-dc-x64.