be-go: invalid configuration can trigger unhandled exception

[Byron]

When package.alias is set to something unknown in the package database.

ERROR:be:An unhandled exception occurred
Traceback (most recent call last):
  File "[..]dependencies/lib/bcore/latest/noarch/src/python/bcmd/base.py", line 315, in parse_and_execute
    return self.execute(parsed_args, remaining_args)
  File "[..]dependencies/lib/bcore/latest/noarch/src/python/bcmd/base.py", line 195, in execute
    return cmd.execute(args, remaining_args)
  File "[..]dependencies/lib/bcore/latest/noarch/src/python/bprocess/plugins/be_go.py", line 92, in execute
    programs = self._executable_package_names()
  File "[..]dependencies/lib/bcore/latest/noarch/src/python/bprocess/plugins/be_go.py", line 80, in _executable_package_names
    package = ProcessController._resolve_package_alias(package, lambda n: self._to_package(n, packages[n]))
  File "[..]dependencies/lib/bcore/latest/noarch/src/python/bprocess/controller.py", line 668, in _resolve_package_alias
    package = fpackage_by_name(package.data().alias)
  File "[..]dependencies/lib/bcore/latest/noarch/src/python/bprocess/plugins/be_go.py", line 80, in <lambda>
    package = ProcessController._resolve_package_alias(package, lambda n: self._to_package(n, packages[n]))
KeyError: 'omcopy-exec'