refactor: set lxcfs managed by systemd

[CodeJuan]

Ⅰ. Describe what this PR did

To improve availability, lxcfs process should be managed by other process, such as systemd.

Ⅱ. Does this pull request fix one issue?

NONE

Ⅲ. Describe how you did it

1. Remove the code of starting lxcfs in Pouchd.
2. Check if the mount point of lxcfs is existed when starting Pouchd.

Ⅳ. Describe how to verify it

1. Make sure lxcfs is running, and the mount point of lxcfs is /var/lib/lxcfs
2. pouchd --enable-lxcfs
3. pouch run -m 512M --enableLxcfs=true registry.hub.docker.com/library/busybox:latest head -n 1 /proc/meminfo
4. The output should be 524288 kB

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #885 into master will decrease coverage by 0.03%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #885      +/-   ##
==========================================
- Coverage   14.62%   14.58%   -0.04%     
==========================================
  Files         115      116       +1     
  Lines        6940     6958      +18     
==========================================
  Hits         1015     1015              
- Misses       5839     5857      +18     
  Partials       86       86

Impacted Files	Coverage Δ
cli/remount_lxcfs.go	0% <0%> (ø)
cli/main.go	0% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d3c2f20...e9f5177. Read the comment docs.

[Letty5411]

hack/make.sh also need to be edited to install fuse.

[Letty5411]

also need to change ./package/deb/systemd/pouch.service

[HusterWan]

LGTM

[jcxian]

@Letty5411 I modify the service file like you do, but after restarting lxcfs, still can't see the file /proc/meminfo in the container. This error still exists. “cat: /proc/meminfo: Transport endpoint is not connected”

[xigang]

The same problem. After starting the lxcfs service,Execute the following mount command:

in container:

# cat /var/lib/lxc/lxcfs/proc/cpuinfo
cat: /var/lib/lxc/lxcfs/proc/cpuinfo: Transport endpoint is not connected

@CodeJuan @Letty5411 Please help😁

[xigang]

https://github.com/xigang/lxcfs-admission-webhook/blob/dev/script/container_remount_lxcfs.sh