add git versioning for topotests

[pguibert6WIND]

Is it possible to use some versioning on topotests. The goal is to be aware of the topotest version currently tested for users.

topotests has features that are added. speaking with topotests version is nicer than speaking with sha1.

my proposal is to set a tag 1.0 for instance on one of the next commits merged on topotests master.

we could then align with versioning workflow with frr:

• new features : 1.0 => 2.0
• bug fixes : 1.0 => 1.1 ( not for each commit, it is a maintainers decision, I think).