Migrate Maven Merge job to global-jjb

Migrate Maven Merge job to global-jjb

Provide a Maven Merge job that is generically reusable by other
projects. This new job uses cURL to upload artifacts to Nexus and uses
`wget -r` to mirror existing maven-metadata.xml files in order to update
them when pushing SNAPSHOTs.

This job uses the following strategy to deploy jobs to Nexus:

1. `wget -r` to fetch maven-metadata.xml from Nexus
2. `mvn deploy -DaltDeploymentRepository` to prepare files for upload
3. Removes untouched maven-metadata.xml files before upload
4. Use lftools (cURL) upload script to push artifacts to Nexus

Issue: RELENG-61
Change-Id: I7663731d0eb750e4ccc1b07bcf5ad39c6135900c
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>