[cubicweb-ctl] respect sys.exit status code when aborting a command When exploring the stack of all calls to a cubicweb-ctl command, it has been discovered than on a KeyboardInterrupt and on a SystemExit exception the base class InstanceCommand (for commands that works on one instance) will always set the return code of cubicweb-ctl to 8: this mean that if another command do a `sys.exit(some_code)` the exit code will be ignored and overwritten by '8'. This behavior is not intuitive, apparently not documented and doesn't seems to have any justification. It also prevent commands from exciting with different return codes which could be a desired behavior in the situation of scripting.

^build$
^dist$
\.egg-info$
^.tox$
^.cache$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
\.pybuild
cubicweb/server/test/data/slapd.conf
debian/python-cubicweb
debian/*.log
debian/*.substvars
debian/cubicweb-doc
debian/cubicweb
debian/files

syntax: regexp
.*/data.*/database/.*
.*/data/ldapdb/.*
.*/data/uicache/
.*/data/libpython/cubicweb_.*/i18n/.*\.po
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/
^doc/_build
^doc/js_api/
test-results.xml
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