Improve rancher-selinux version parsing logic

[andypitcher]

The current version parsing logic is not straight forward, this issue is created to remodel it.

Elements to take into consideration:

• SELinux Policies are usually versioned, see container-selinux's policy tags and versions
• Map the policy version with the tag version

cc @macedogm

[macedogm]

We should also check how SUSE version their own SELinux policies and use that as a base for us - https://build.opensuse.org/package/show/openSUSE:Factory/selinux-policy .

[pjbgf]

A key thing to take into account here is that ideally we would bind together our policy version with our release versions. Given that the later is a whole major ahead, this may mean that the alignment could be made when cutting a 1.1.0 or a 2.0.0 release.

To ensure the same policy version is being used across the supported OSes, ideally we would add some checks so that we can't merge a PR that only bumps some of the policies.