[Trusty][SRU] Increase shutdown time of NVMe devices

[Alex Hung]

SRU Justification:

Impact: According to hardware vendor, short shutdown time can cause the 
disk goes in to rebuild during next power and result in OS finding the device
not responding.

Fix: This patch increases the delay from 2 seconds to 5 seconds. This is
also the default timeout in Windows

BugLink: http://bugs.launchpad.net/bugs/1465136