static slaves: Perform global-jjb init

static slaves: Perform global-jjb init

global-jjb was recently bumped to 0.51, which assumes
jenkins-init-scripts were already executed on the build slave
(e.g. by sourcing ~jenkins/lf-env.sh), which is always true for
Openstack instances dynamically spawned by Jenkins, but not yet
for static slaves like AArch64 dev/build/baremetal PODs.

Add a new job, triggered on ci-management gerrit merge (only if
global-jjb reference is changed) that executes the jenkins-init-scripts
similar to dynamic slaves initialization.

NOTE: Since jenkins-init-scripts are not fully idempotent, some
actions (e.g. id_rsa keypair generation) are executed even though
they are not mandatory (for the id_rsa keypair this means the
private/public keys will be forcefully regenerated each time this new
job runs).

Change-Id: I62433a45c7966aed1d1184fa60e87ee4211996e4
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>