Make port unmapping errors non fatal.

Make port unmapping errors non fatal.

In some cases port unmapping can fail. This should not be fatal nor need client
recovery code.

This can happen when multiple instances of the Forwarder class try to map/unmap
a same port. While the host_forwarder daemon supports that, the python wrapper                                                                                                                                                                                                                                                 
didn't.

R=bulach@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=210306

[Philippe, 2013-07-05 14:19:19]

FYI Marcus, this is needed to fix the ToT bot downstream.

[bulach, 2013-07-05 14:23:43]

lgtm

just checking: what are the conditions which this would fail? i.e., the port was
already unmapped / closed (which is fine to ignore), or something happen and the
port will be left lingering (which may introduce problems later on)?

[Philippe, 2013-07-05 14:29:36]

On 2013/07/05 14:23:43, bulach wrote:
> lgtm
> 
> just checking: what are the conditions which this would fail? i.e., the port
was
> already unmapped / closed (which is fine to ignore), or something happen and
the
> port will be left lingering (which may introduce problems later on)?

Thanks Marcus! This is the former, there seem to be multiple instances of the
Forwarder class trying to map/unmap port 8000. While the host_forwarder daemon
supports that, the python wrapper didn't. I will update the CL description.

[Philippe, 2013-07-05 14:33:49]

Committed patchset #1 manually as r210306 (presubmit successful).