Update tag before creating snapshot packages in Jenkins

Every commit in Jenkins creates a snapshot with the version information using a hard-coded tag. This creates problems in that we have a patch on 3.3.4, but the package generated is named something like:

`CouchbaseNetClient.3.3.1-pre--gerrit--r6009.nupkg`

which is confusing for customers, because they think that they are downgrading if they are on 3.3.4.

This ticket is to improve the naming so that the latest tag is used as a base for the snapshot name. A couple of examples of how to get this info (there are other ways as well):

Jeff Morris@JeffMorris-0503 MINGW64 ~/source/couchbase-net-client ((a5734fc1...))

$ git tag --sort=taggerdate | tail -1

3.3.4

Jeff Morris@JeffMorris-0503 MINGW64 ~/source/couchbase-net-client ((a5734fc1...))

$ git describe --tags $(git rev-list --tags --max-count=1)

3.3.4

Jeff Morris@JeffMorris-0503 MINGW64 ~/source/couchbase-net-client ((a5734fc1...))

$ git tag | sort -g | tail -1

3.3.4

Note: the extra "-" should also be removed from the name.