[FLOC-4557] Bind mount /dev into the lsblk test container

[wallrj]

Fixes:

• https://clusterhq.atlassian.net/browse/FLOC-4557
• https://github.com/ClusterHQ/flocker/issues/2970

Bind mount /dev into the lsblk test container so that multi-path devices can be examined.

@shay-berman please test this modified version of the acceptance test with your IBM driver.

I dug into the Docker and runc code to understand how /dev gets populated inside the container. See the comments and links in the patch.

[shay-berman]

I just planned to push that fix to the project(for my first flocker contribution) but you did that first :-)

[wallrj]

@shay-berman great minds think alike :-)

Let me know how your testing goes.

The tests still seem to pass on with the Loopback driver on Centos7, Ubuntu 16.04 and Ubuntu 14.04

• http://ci-live.clusterhq.com:8080/job/ClusterHQ-flocker/job/FLOC-4557-dev-mapper-blockdevice-size/job/run_acceptance_loopback_on_AWS_Ubuntu_Trusty_for_flocker.acceptance/1/testReport/flocker.acceptance.endtoend.test_dockerplugin/DockerPluginTests/
• http://ci-live.clusterhq.com:8080/job/ClusterHQ-flocker/job/FLOC-4557-dev-mapper-blockdevice-size/job/run_acceptance_loopback_on_AWS_Ubuntu_Xenial_for_flocker.acceptance/1/testReport/flocker.acceptance.endtoend.test_dockerplugin/DockerPluginTests/
• http://ci-live.clusterhq.com:8080/job/ClusterHQ-flocker/job/FLOC-4557-dev-mapper-blockdevice-size/job/run_acceptance_loopback_on_AWS_CentOS_7_for_flocker.acceptance/1/testReport/flocker.acceptance.endtoend.test_dockerplugin/DockerPluginTests/

[wallrj]

See https://github.com/docker/docker/issues/16160 for more discussion of why /dev inside the container does not have all the devices that are available on the host server.