Break boostrap.sh into pieces

Break boostrap.sh into pieces

In order to make it easier for folks who have existing
Centos or Ubuntu boxes to utilize the same
'Getting started' scripting that is used in Vagrant,
as well as enable us to use that scripting in CI,
broke up bootstrap.sh into

update.sh - Things like apt-get update
build.sh - Install any dependencies and build vpp
clearinterfaces.sh - Clean off any non-default gateway
                   interfaces.  Used by vagrant.
run.sh - Start vpp as a service on the box.

A user (or CI) just wanting to get going and build
on an existing Ubuntu or Centos image (ie, not via
vagrant) can simply run

build.sh

Change-Id: I8f19342f163cad07c6c05def943a5fb8e394b879
Signed-off-by: Ed Warnicke <eaw@cisco.com>