Install which on Fedora

Create an install hook where core utilities can be installed
on Fedora. In this case we are installing which.
Which is being used by
  ramdisk/post-install.d/01-ensure-binaries
  vm/finalise.d/51-grub
The absence to which caused the ramdisk build to fail on F19.

On Ubuntu which is installed with the package debianutils, this pretty
much has to exist on Ubuntu images, so a corresponding package install for
ubuntu isn't needed.

Fixes Bug 1202612

Change-Id: I847c1619cdab021c9348caed3fa32db64e663e8e
Merge "Install which on Fedora"