Don't continue to execute after an ImportError

[matthewfeickert]

This is an antipattern, by the way. The Python core devs specifically say it’s invalid to continue executing after an ImportError. (In the core.py podcast) — @henryiii

recast-atlas/src/recastatlas/backends/__init__.py

Lines 16 to 43 in 11af091

	BACKENDS = {}
	try:
	from .reana import ReanaBackend
	BACKENDS["reana"] = ReanaBackend()
	except (ImportError, exceptions.BackendNotAvailableException):
	pass
	try:
	from .kubernetes import KubernetesBackend
	BACKENDS["kubernetes"] = KubernetesBackend()
	except (ImportError, exceptions.BackendNotAvailableException):
	pass
	try:
	from .local import LocalBackend
	BACKENDS["local"] = LocalBackend()
	except (ImportError, exceptions.BackendNotAvailableException):
	pass
	try:
	from .docker import DockerBackend, setup_docker
	BACKENDS["docker"] = DockerBackend()
	except (ImportError, exceptions.BackendNotAvailableException):
	pass

So need to find a better way to discover what execution backends are available for use.