Fix test export into nitrate on rhel-8 [fix #337]

Do not use capture_output as it is a Python 3.7+ feature.
Use dict_to_yaml() to prevent the one-line json fmf id.

tmt/base.py

@@ -89,7 +89,7 @@ def fmf_id(self):
 
  def run(command):
  """ Run command, return output """
- result = subprocess.run(command.split(), capture_output=True)
+ result = subprocess.run(command.split(), stdout=subprocess.PIPE)
  return result.stdout.strip().decode("utf-8")
 
  fmf_id = {'name': self.name}

tmt/export.py

@@ -165,9 +165,9 @@ def export_to_nitrate(test, create, general):
  echo(style(section + ': ', fg='green') + attribute.strip())
 
  # fmf identifer
- fmf_id = test.fmf_id
- struct_field.set('fmf', yaml.dump(fmf_id))
- echo(style('fmf id:\n', fg='green') + yaml.dump(fmf_id).strip())
+ fmf_id = tmt.utils.dict_to_yaml(test.fmf_id)
+ struct_field.set('fmf', fmf_id)
+ echo(style('fmf id:\n', fg='green') + fmf_id.strip())
 
  # Warning
  if WARNING not in struct_field.header():