Increase watermark sleep in tests for reliability.

The nodepool tests depend on watermark sleep being long enough that all
of the fake nodes are marked ready before the next deficit check. If it
is not long enough then the tests may boot extra servers causing asserts
in tests to fail.

Increase watermark sleep to one second from half a second and let each
test sleep for three seconds before checking node states.

Change-Id: Ia94527b46bad26b184af8fa02b3a1e2a1f7a3430