add GerritChangeFilter

Its not very clear for people how to use gerritchangesource to filter
gerrit change events, and create builds.

add GerritChangeFilter, which is a simple general purpose filter, which
manage most of the changefilters needs

doc + tests

and some whitespace fixing in the doc.

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
gerritfilterbranch: more factorization

This comes at the prize of a little bit of complexity

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
gerritchangesource: fix grouping for Nightly schedulers

for nightly and post-commit style schedulers,
you really need to have the branch to be the real gerrit branch
or the list of changes in the UI will be incorrect

This is a simple way of implementing it, probably by separating the
change grouping to the notion of change branch

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
gerritchangesource: test branch is branch for event type != changeset-created

and some cleanup of failUnless* API usage

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>
Fix shell hangs on checkconfig command when using http steps
Add sharedSession to prevent blocking session
Fix restart hang, close session at the end of the reactors
Add request status code as description step is  done
Add content log
Fix httpstep tests
Fix W293 blank line contains whitespace
Update index before applying try patch with git.
Ignore E123 since it's ignored in nine
ignore E123 in autopep8, too
remove outdated note about MySQL temporary tables
new step is VS2013, not VS2014
Merge branch 'buildbot-0.8.9'
Wrong error messages for a failed rebuild
Merge jaredgrubb/buildbot:bug-wrong-error (PR #1139)
Wrong error messages for a failed rebuild