Add logging information to lable based discover

See merge request !107

This will show information similar to the describe based
implementation.

Implement environment discovery using docker labels

See merge request !106

The next release of BEAT environments will make use of docker
labels to provide the information the current describe command
returns (minus the os entry which is not currently used).

This new implementation of discovery uses these labels and thus
speeds up the process.

The original code is kept as a fallback method in case a node only
has images using the old build process.

Remove loops from representation in toolchain schema

See merge request !105

The blocks entry covers them as it already covers both
the blocks and analysers. Therefore there's no need for
an additional property here.

Completely remove "license_file" entry on conda recipe

Closes #91

See merge request !104

See bob.devtools#44 and bob.devtools!127

Improve protocol template lookup for database prototype

Closes beat.editor#249

See merge request !103

Rather than blindingly selecting the first protocol template
found, look for the first valid one.

[docedit] removed Biometrics evaluation from the definition of BEAT

See merge request !102

Move conda related helper methods out of test class

See merge request !101

That will make them re-usable in other tests like
in beat/beat.cmdline>

Subprocess execution with different environment

Closes #90

See merge request !100

This test tends to fail on macOS with Python3.7

It is however unclear why as the test passes most
of the time. Especially in the other CI environments.

test_execute in test_bcp fails for unclear reasons
from time to time. Add flaky to allow re-running the
test automatically in case it's just a glitch.

This patch implements a new parameter that allows to pass
the path to the python executable of the environment one
would like to use to execute an experiment. The various
beat/beat.backend.python from that environment will be
called in place of the current environment as it is
by default.

Fixes #90

Dependencies cleanup

See merge request !99

Needed for matplotlib image output

It's only used by the plotters in the prefix.

Update test loop evaluator write method signature

See merge request !98

Following beat.backend.python!61 the method has
now a third argument containing the output currently
written to on the processor side.

Remove rogue print statement

See merge request !97

Improve error handling on algorithm local execution

See merge request !96

Currently, when an error occurred in one of the scripts, it
could just hang or the error itself wasn't properly processed.

This patch improves exception handling as well as error
message returned.

Tests improvements

See merge request !95

Like this the test passes but is known to trigger
the issue described in beat.backend.python#26
and fixed by beat.backend.python!59.

This makes the validate part more coherent.

Improve two_loops test experiment

See merge request !94

Without that some tests might stale indefinitely.