fix(cgroup): fix parse zero or multi optional fields in mountinfo

[PureWhiteWu]

There could be zero or more optional fields in mountinfo according to https://man7.org/linux/man-pages/man5/proc.5.html

And also there's some minor code cleanup.

[PureWhiteWu]

In addition, I think this is a critical bug, which may cause performance greatly affected in containers(in fact, we are encountering this bug in our production environment).
Could you please publish a new version after this is merged?
Thanks a lot.

[seanmonstar]

Thanks for the PR! A problem we currently have is that the CI is no longer active on new PRs. We need to move off Travis-CI, and probably onto Github Actions.

[PureWhiteWu]

Thanks for the PR! A problem we currently have is that the CI is no longer active on new PRs. We need to move off Travis-CI, and probably onto Github Actions.

Okay, I've already sent another PR #114 to set up github actions.
You may need to enable the workflows and remove travis from your config.

[seanmonstar]

Ok, so I think if you rebase this branch off master, we'll get the proper CI going...

[PureWhiteWu]

Seems that Rust 1.13 is too old, can we update it to a newer version?

[PureWhiteWu]

I've tested and found that this requires a minimal version of 1.22, so I changed to version in ci to 1.22.
This can make code much more easier to read and write, so I think this upgrade is worthwhile.

[seanmonstar]

In general, I've taken a conservative approach to MSRV upgrades, and only done so when a new thing in Rust was needed to provide essential functionality. What is needed here that's new? Is it just if let Some(..) = syntax? We could just use match and keep the MSRV.

[PureWhiteWu]

I've fixed that on 1.13 and it should be fine now.
FYI, the feature I used that doesn't support 1.13 is the two below:

1. https://github.com/seanmonstar/num_cpus/pull/113/files#diff-8eb8a5676963047d3171ac963ed5ade2b14abf02ba028c01b9dfee133a70c0cbR243
2. https://github.com/seanmonstar/num_cpus/pull/113/files#diff-8eb8a5676963047d3171ac963ed5ade2b14abf02ba028c01b9dfee133a70c0cbR302

After this is merged, could you please release a new version?

[seanmonstar]

And release as v1.13.1. Thanks for the work!