os.(open|write|close) are used in several places without consideration for EINTR

[Gavin Panella]

bzr grep '\bos[.](open|close|read|write)\b'

From what I understand EINTR ought to be dealt with as a normal part of working with os.open, .close and especially .read and .write. Several parts of Launchpad, including ssh/sftp support in lp.poppy and lp.codehosting, do not, and would crash if EINTR were to be encountered.

I don't know how important this is, so someone who has more of a clue can can triage or close it. It obviously doesn't seem to be kicking us much right now.