OpTestUtil.py: Increase login expect timeout
OpTestUtil.py: Increase login expect timeout

Sometimes the login prompt takes more time to login and the times out
before expecting last login: prompt, so increased the timeout

Signed-off-by: Abdul Haleem <d72979407b2438b90c42979d11f88d04d190c5d3@linux.vnet.ibm.com>

open-power/op-test-framework,open-power/op-test-framework,open-power/op-test-framework