script: add lib-build.sh for common high level funcs and no main

script: add lib-build.sh for common high level funcs and no main

The intention of this file is collect some of the most basic or common
shell functions used across the various build scripts.
I would also like to ensure that functions added here are validated
using `shellcheck`. Currently, there's no automation for this, just
the honor system, but eventually we can start automating validating
this and other scripts with shellcheck.

Signed-off-by: John Mulligan <jmulligan@redhat.com>
(cherry picked from commit 29d9a827e7396dcdc51b124f3e40e3144fa9ccb9)