Set GRUB_HIDDEN_TIMEOUT=5 in /etc/default/grub

* This gonna give some time to VM to make
  hard drives fully available. Othewise kernel
  could encounter VFS syncing issue. This case
  is quite hard to reproduce.

Change-Id: I2128f5b0a894231454b5bcc540b8991394f89ed4
Related-Bug: 1396078
Merge "Set GRUB_HIDDEN_TIMEOUT=5 in /etc/default/grub"