Create Maven release job

Create Maven release job

The Maven release job runs a build and deploys the artifacts into a
local staging repository located at $WORKSPACE/m2repo which is then
used to push to a Nexus staging repository later in the build process.

- Adds a new Maven release job
- Merges the maven-exec macro into a single lf-infra-maven-parameters
  macro.
- Creates a common-variables.sh which can be sourced for useful common
  variables.
- Store staging-repo number in archives staging-repo.txt for easy
  retrieval.

Change-Id: I020d819ea59b809d06803c0dfd999ef002b201c4
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>