Specify --suppress-sync when running package managers

Specify --suppress-sync when running package managers

Package managers tend to make sure of sync() and friends to ensure
that any files they write are actually written to disk. This is
important when a package manager is used to do system package upgrades,
but is unnecessary when using package managers to build OS images. So
let's make sync() and friends a noop when we invoke package managers

Replaces #3544