1568092: Also check syscall.Errno in getMessageFromErr

[cherylj]

This test could've been skipped since lxd is not currently
supported on Centos, but I added the check for the
syscall.Errno to reduce the number of skips that we have.

This was live tested on Ubuntu and CentOS and tests passed
on both.

(Review request: http://reviews.vapour.ws/r/4501/)

[cherylj]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Does not match ['fixes-1568312']
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/7276

[cherylj]

$$JFDI$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/7277

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/7278

[jameinel]

$$merge$$