nmci.util: support with statement with timeout
Add support for the following code:
with nmci.util.start_timeout(10, "wait for something") as t:
while t.loop_sleep(0.2):
if something():
break
In case something() does not return anything meaningfull in 10s, there will be assert "Timeout 'wait for something' expired in 10.000s".
Edited by Filip Pokryvka