Add patching QA configuration files on buildbots

In order to work, it is necessary:
* Write a JSON Patch to file "qa/qa-patch.json" in a source repository.
  (And be careful not to commit it!) The file must conform to RFC6902
  and describes what changes should be done to the QA JSON
  configuration. This is simple as
   [
     { "op": "add",
       "path": "default",
       "value": false },
     { "op": "add",
       "path": "/tests/instance-add-file",
       "value": true }
   ]

* Install "jsonpatch" and "jsonpointer" modules on the machines QA is
  running on. Either using "easy_install" or as Debian packages using
  "pypi-install".

QA only loads the modules if the patch file is present and non-empty.
Therefore no changes to buildbots are needed, if the feature is not
used.

It's advisable to add a git pre-commit hook for the main repository to
prevent changes to "qa/patch.json", keeping it to "[]". Suggestion for
such a hook:

  # Exit code 1 if the patch file isn't just "[]":
  python -c 'import json, sys; \
    exit(0 if json.load(open("qa/qa-patch.json", "r")) == [] else 1)'

Locally it's possible to tell git not to track changes to the file at
all (see https://help.github.com/articles/ignoring-files):

  git update-index --assume-unchanged qa/qa-patch.json

Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>
Fix broken TAGS generation

This file is used for development to point to code definitions. Apparently this
has been broken since Februrary [cc40185]. The improved version fixes the
problem and uses Exuberant Ctags <http://ctags.sourceforge.net/>. It uses
"etags" instead of "ctags", so Emacs compatibility should be maintained.

The extra suffixes "-osuf" and "hisuf" are used to avoid problems with already
compiled object files.

Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Jose A. Lopes <jabolopes@google.com>
build_chroot: hard-code the version of blaze-builder

The newest version does not build on debian squeeze, so avoid
it beeing pulled in as a dependency.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Jose Lopes <jabolopes@google.com>