test-network: convert wait_operstate() to recheck condition for timeout seconds

test-network: convert wait_operstate() to recheck condition for timeout seconds

Failing after a single check leads to extra sleeps scattered through
test cases, and can also lead to false failures.  Instead perform a
recheck for a number of seconds until the state matches, and fail only
if the timeout is exceeded.

This allows removing all the manual sleeps in the testcases.