Changes

contrib/ci.inria.fr: fix the retrieval of the current branch name
If the workspace clone ever ran on another branch (e.g. in my zbgoglin
jobs), git branch returns multiple lines, which causes the 2nd branch
name to be ran as a command-line after the only expected line
"job-0-tarball.sh <firstbranch>"
Use git rev-parse --abbrev-ref HEAD instead.
Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
(cherry picked from commit 8f132f5dfd48b9035d9a60e7c69b5f1bfa0d77ad)