Add minimal rw tmpfs for /tmp and /run

Closes #101

See merge request !125

At least in production, some issues happened that required
to have /tmp writable. To preserve the read-only state
of the container, use a small tmpfs that is enough for
the container to run. /run is another that might be needed
so make it part of the defaults used.

Add test for setup in cxx algorithm

See merge request !124

This test ensures that the setup feature works properly.

Ensure that writing to a non existing output shows an error

See merge request !123

It has been the case for a while for beat/beat.backend.cxx>

- beat.env.python.tests 1.3.0r7
- beat.env.db.examples 1.4.0r7
- beat.env.cxx 2.0.0r4
- beat.env.cxxdev 2.0.0r4

Add optionnal environment entry to database

See merge request !122

This makes use of the new environment field that can be
added to the database declaration and is then used to
select the runtime environment in place of the database
search done until now.

This replaces the database name based search.

This field will allow to specify which environment should
be used to use a database. If not present, the old detection
process is used.

Fix database prototype

Closes #97

See merge request !121

This ensure that the setup call is properly done

Move to new images

See merge request !120