Create tools/install_prereqs.sh

* Factor system package prereq installs out to tools/install_prereqs.sh
* Set minimum time between runs with PREREQ_RERUN_HOURS
  default = 2 hours
* Create re_export_proxy_variables

Change-Id: I4a182b1da685f403d6abdd8540d2114796c01682
Holiday docs and comment formatting cleanup

Change-Id: Ia4ca88c67d3b94e306a79a669805a2fa1b0dc069
Merge "Create tools/install_prereqs.sh"