[#2123] AIX dev buildslave setup.

Why?
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Because we need an AIX dev buildslave.


Solution?
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Update the AIX bits in `chevah-os-bootstrap`.


How to check?
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Please review changes.
On a freshly installed AIX 5.3+ machine execute the `bootstrap.sh` script as root.
Login as the newly created user `chevah` and execute `git.sh` to get git working.

reviewers: @adiroiban