Version lock kernel after removing old kernels

[cartermckinnon]

Issue #, if available:

Description of changes:

This fixes an issue with multiple version locks on the kernel package, which may result in unexpected behavior when installing/updating this package.

This PR moves the version lock after old kernel packages have been removed, as well as explicitly locks the running kernel.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Testing Done

Before this change, a version lock was present for both 4.14 and 5.4 versions of the kernel:

> yum versionlock list
Loaded plugins: priorities, update-motd, versionlock
0:kernel-4.14.301-224.520.amzn2.*
0:kernel-5.4.228-132.418.amzn2.*
0:runc-1.1.4-1.amzn2.*
0:containerd-1.6.6-1.amzn2.0.2.*
0:docker-20.10.17-1.amzn2.0.1.*
versionlock list done

The version lock on the 4.14 kernel is removed after this change.

> yum versionlock list
Loaded plugins: priorities, update-motd, versionlock
0:kernel-5.4.228-132.418.amzn2.*
0:runc-1.1.4-1.amzn2.*
0:containerd-1.6.6-1.amzn2.0.2.*
0:docker-20.10.17-1.amzn2.0.1.*
versionlock list done