add support for testing execin

when the test binary starts, it detects whether it should run the container
initialization code or the execin initialization code based on the suppplied
arguments. The execin initialization code is taken from docker.

also added a sample test for execin process.

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
execin should honour rlimit of the container

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
refactor common container setup out of execin tests

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
Merge pull request #287 from dqminh/execin-test

add support for testing execin
add spec for exec a new process inside a container

document desired execin process behavior for v1 container specification

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
cgroup: add support to set MemorySwap

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
user: MAINTAINERS: add cyphar as a maintainer

This patch adds Aleksa Sarai to the maintainer list for libcontainer's
user API.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> (github: cyphar)
fix some grammar errors

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
Merge pull request #288 from hqhq/hq_add_memory_swap

cgroup: add support to set MemorySwap
move cgroup requirements to planned additions

also document that the executor will only try to remove all the children in a
best-effort way.

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
Merge pull request #289 from dqminh/execin-rlimit

Set rlimit for execin process
cgroups: add failcnt test

It was missed in the first place.

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
Merge pull request #295 from hqhq/hq_fix_memory_test

cgroups: add failcnt test
Merge pull request #294 from cyphar/user-add-cyphar-maintainer

user: MAINTAINERS: add cyphar (myself) as a maintainer
Merge pull request #290 from dqminh/exec-spec

add spec for exec a new process inside a container