aemfvp-a-rme: script for booting and installing distro in FVP

added distro.sh script to allow a distro's raw or iso image to be installed
or booted at FVP. Changes include
- support installation of distro iso images at FVP with a generated satadisk
  to install the image on with params -i <image> -s <satadisk_size>
- allow a pre-installed satadisk or a distro raw image to be booted at FVP
  using param -d <disk image>
- automated use case supported in boot scenario, where xterm logs are collected
  and FVP is killed after boot is complete and login prompt appears.

Signed-off-by: nitin sharma <nitin.sharma3@arm.com>
Change-Id: Ife8368527c213474cdf9f7881f0ae9b5b35b029b

Change-Id: I6081129725188662388e2ea8fcc34f4f01bf8a14