Name already in use

Reprotest wasn't aware of the host toolchain settings for the
adt_testbed module. Add a command-line argument and propagate it to
start_testbed so users can choose a specific toolchain for their
distribution. Ideally, in the future, this host-toolchain could be
guessed on runtime.

The distro toolchain was hardcoded for debian. Now that two modules
provide an abstraction, add a keyword parameter to load the toolchain
for a specific distro.

Note that, at this point, this parameter is ignored by the reprotest
script.

Arch requires a different system_interface abstraction than Debian. Add
an arch-specific module to handle the required calls from adt_testbed.

Many distros may want to use reprotest and the current implementation
depends on the Debian toolchain. Abstract away the debian-specific
toolchain to a separate module, and provide a way to extend this for
cross-distro compatility.

Many functions within adt_testbed weren't hit by the execution paths
(given that the adt_testbed code is reused from autodeptest, which has a
broader scope than reprotest). Remove the unused code from the
adt_testbed module in order to increase readability and maintainability.

Functions such as TempPath and killtree could (and will probably) be
used by the system interface modules. Factor them out to a separate
module so they can be used in the system interfaces.

Signed-off-by: Holger Levsen <holger@layer-acht.org>

Otherwise `find` can't find the artifacts, to calculate their hashes

Signed-off-by: Chris Lamb <lamby@debian.org>

Signed-off-by: Chris Lamb <lamby@debian.org>

… missed in the future

… flag

- build_command is a string now
- don't error if certain config keys are not set

… --store-dir is not given