test-timesync: add first test for timesyncd conf parsing

test-timesync: add first test for timesyncd conf parsing

We parse the string supplied in NTP_SERVERS during configuration under an
assert_se(). Right now we will accept pretty much anything there, but in case
we are more picky in the future, add a simple test which checks that we can
actually parse whatever is in NTP_SERVERS so that we don't fail the assertion
at runtime.