fabric switch_user content manager

from contextlib import nested
from fabric.api import task, run, settings, env

def switch_user(user):
    return nested(settings(
        user=user,
        host_string="%s@%s:%s" % (user, env['host'], env['port'])
    ))

@task
def install():
  with switch_user('foobar'):
    run('whoami')  # => foobar