Allow setting Linux kernel parameters (sysctl) via settings

[tjkirch]

Issue number:

Fixes #1125

Description of changes:

It would make sense to look at these commits separately.

The Cargo.lock V2 format change is a separate commit so that it's clear there were no real changes to dependencies:

    Update sources/Cargo.lock to V2 format

The second commit is a bug fix for schnauzer that's required for sysctl settings; we hadn't previously sent quoted keys through metadata queries:

    schnauzer: percent-encode query parameters going to apiserver
    
    This lets us handle quoted keys, e.g. settings.kernel.sysctl."vm.max_map_count"

The main event:

    Allow setting Linux kernel parameters (sysctl) via settings

Testing done:

[ec2-user@ip-192-168-18-172 ~]$ apiclient -u /settings -X PATCH -d '{"kernel": {"sysctl": {"vm.max_map_count": "262144", "user/max_user_namespaces": "16384"}}}'
[ec2-user@ip-192-168-18-172 ~]$ cat /proc/sys/user/max_user_namespaces
0
[ec2-user@ip-192-168-18-172 ~]$ apiclient -u /tx
{"kernel":{"sysctl":{"user/max_user_namespaces":"16384","vm.max_map_count":"262144"}}}
[ec2-user@ip-192-168-18-172 ~]$ apiclient -u /tx/commit_and_apply -m POST
["settings.kernel.sysctl.\"vm.max_map_count\"","settings.kernel.sysctl.user/max_user_namespaces"]
[ec2-user@ip-192-168-18-172 ~]$ apiclient -u /tx
{}
[ec2-user@ip-192-168-18-172 ~]$ cat /proc/sys/user/max_user_namespaces
16384
[ec2-user@ip-192-168-18-172 ~]$ cat /proc/sys/vm/max_map_count
262144

I also used the user data example that I added to README, and saw the instance come up with the two requested sysctl settings set.

[settings.kernel.sysctl]
"user.max_user_namespaces" = "16384"
"vm.max_map_count" = "262144"

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[tjkirch]

^ This push fixes the issues found by @zmrow.

[tjkirch]

^ This push fixes some concerns raised by @bcressey:

• log rather than error when we can't write a sysctl value, to ease management (see comment)
• add tests showing no directory traversal, and add double-check on input

[zmrow]

🍁