ec2 needs to handle EINTR

Starting an ec2 test gave me:

utilities/shhh.py PYTHONPATH= ./bin/buildout \
                configuration:instance_name=development -c bTraceback (most recent call last):
  File "/home/jw2328/devel/launchpad/nuke-code-import-warts/lib/devscripts/ec2test/instance.py", line 426, in set_up_and_run
    retval = func(*args, **kw)
  File "/home/jw2328/devel/launchpad/nuke-code-import-warts/lib/devscripts/ec2test/testrunner.py", line 504, in run_tests
    user_connection.perform(' '.join(cmd))
  File "/home/jw2328/devel/launchpad/nuke-code-import-warts/lib/devscripts/ec2test/instance.py", line 603, in perform
    select.select([session], [], [], 0.5)
error: (4, 'Interrupted system call')

which killed the process and I had to start again from the beginning.

Thanks,

James