FileNotFound is Python 3 only, therefore use its base class
to be compatible with both versions of Python.

Make raise_on_errors a member and use it in _exec

See merge request !24

This allows to be coherent when running a command and docker is not
installed.

For example _discover_environment will fail even if raise_on_errors is
set to False if docker is not installed. This patch fixes that.

Schema changes

See merge request !22

[dock] Closes #55 by restricting the image search to images with the name containing `beat.env.`

See merge request !23

This reverts commit 85cef289.

Changes for BEAT editor support for Graphviz toolchain layout

See merge request !21

Both are currently used by beat.web in the buildout process and
can also be used when developing the package locally.

New Conda-based CI/CD Pipelines

See merge request !19