Add an easy function for synchronous calls

Add an easy function for synchronous calls

The added function, 'jobs_call', allows to call
a job with 'group' sequencing and 'timeout'
handling synchronously.

The difference with 'jobs_enter' is that the
function 'jobs_call' assert that the job is
terminated when 'callback' returns.

Change-Id: I8c01d1cd017787ca0448b03a899305a9069ebb6c
Signed-off-by: José Bollo <jose.bollo@iot.bzh>