T5486: smoketest: adjust to new process_named_running() implementation

After commit 9c677c8 ("vyos.util: extend process_named_running() signature
with cmdline") we need an exact match for the process name. In the past
we used a in b and now we test for a == b.

Process name doesn't march 'ddclient'
psutil.Process(pid=10987, name='ddclient - sleeping for 20 seconds', started='13:12:47'
It cause smoketest fail