wait_command.ex: Change `wait` internal sleep to one second

[dumbbell]

... down from 10% of the configured timeout.

This has a significant impact on the time it takes to start RabbitMQ in all our testsuites. rabbitmq-ct-helpers sets a wait timeout of 180 seconds. Thus before this patch, the wait loop would sleep for 18 seconds between each check. Given it takes about 1.5 seconds to start RabbitMQ, a lot of time is wasted here.

Here are some numbers after running testsuites with and without this patch:

• make ct-fast in rabbitmq-server: 8m15s down to 4m58s
• make ct in rabbitmq-mqtt: 9m23s down to 6m43s
• make ct in rabbitmq-stomp: 4m31s down to 2m04s

[michaelklishin]

This is a great find.