fix the order of setns()

Docker-DCO-1.1-Signed-off-by: Takahiro Maebashi <maebashi@iij.ad.jp> (github: maebashi)
namespaces: nsenter: ignore nonexistent namespaces

If a particular kernel doesn't have namespace directories that
libcontainer tries to attain during nsenter(), ignore the error (this is
consistent with the previous implementation of nsenter()).

Docker-DCO-1.1-Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> (github: cyphar)
remove unnecessary headers

Docker-DCO-1.1-Signed-off-by: Takahiro Maebashi <maebashi@iij.ad.jp> (github: maebashi)
Libcontainer fs.GetStats() will not look for cgroups relative to the cgroup of init process if the parent
in cgroups.Cgroup is absolute. This is required to get stats of other containers while running inside a docker container.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Implement system.GetClockTicks for all platforms

Docker-DCO-1.1-Signed-off-by: Bernerd Schaefer <bj.schaefer@gmail.com> (github: bernerdschaefer)
Merge pull request #130 from vishh/fix_cgroup_path

Make fs.GetStats() work when used from inside a docker container.
Merge pull request #133 from soundcloud/non-linux-clock-ticks

Implement system.GetClockTicks for all platforms
Merge pull request #58 from maebashi/fix-setns-order

fix the order of setns()
Move "pkg/user" into libcontainer and add support for GetUserGroupSupplementary to return "Home" too

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #103 from tianon/user

Move "pkg/user" into libcontainer...
Update more "dotcloud/docker" refs to "docker/docker"

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #134 from tianon/fix-more-dotclouds

Update more "dotcloud/docker" refs to "docker/docker"
Add nsenter --config option

Docker-DCO-1.1-Signed-off-by: Dhammika Pathirana <dhammika@gmail.com> (github: dhammika)