Hide it from "git grep" and similar commands.

Export the job configurations XML and verify that the plugin was
executed successfully.

Add the possibility to apply version dependent fix-ups when invoking hook
functions.

The usage of stable paths (/bob/...) has traditionally been bound to the
usage of a sandbox. This makes sense insofar as these virtual paths
depend on the usage of mount namespaces.

The new "stablePaths" option allows to override the usage of virtual,
stable paths. By default, the existing heuristic is retained. But the
usage of stable paths can be now forced or prohibited too.

The slim sandbox uses the bob-namespace-sandbox to restrict access to
workspace paths. But in contrast to the existing "fat" sandbox, a slim
sandbox does not use a sandbox image. To gain at least a bit of
information hiding, the current working directory is hidden behind a
whiteout. This should usually hide all other workspaces.

To introduce different sandbox modes, a SandboxMode helper is added.
This helper controls three different aspects of the sandbox operation:

* slimSandbox: use mount namespaces without a sandbox image.
* sandboxEnabled: usage of the sanbox image
* stablePaths: force or prohibit stable paths

Using these properties, the following sandbox modes are defined:

* no-sandbox
* sandbox: traditional sandbox mode
* slim-sandbox: always isolate, always use workspace path, not use
  sandbox images.
* dev-sandbox: always isolate, always use workspace path, use sandbox
  images if available.
* strict-sandbox: always isolate, always use stable paths, use sandbox
  images if available.

Adds the new --slim-sandbox, --dev-sandbox and --strict-sandbox options
to the dev/build commands.

Let the "sandbox" command default additionally accept the 'no', 'yes',
'slim', 'dev' and 'strict' strings that correspond to the respective
command line options.

Adds the new --slim-sandbox, --dev-sandbox and --strict-sandbox options
to the jenkins commands.

The function actually tests the usage of a sandbox image. This is an
important distinction because it won't return true in case of the slim
sandbox build mode. Likewise, it will return false in the dev- or
strict-sandbox modes when packages have no available sandbox image even
though isolation is applied.

The test incorrectly uses `--dev' as abbreviation for the '--develop'
option. While this worked so far, it will be ambiguous with the
introduction of the '--dev-sandbox' option.

This does not actually add any new behaviour. But it makes the remaining
commands consistent with the build/dev/jenkins commands by accepting the
same options.