install-deps: extract SUDO variable logic into a reusable function

install-deps: extract SUDO variable logic into a reusable function

While the function is pretty simple and could be copy-pasted I
prefer to extract things into functions to indicate that the
logic is used/repeated elsewhere to ward off making changes to
one copy vs the other.

Signed-off-by: John Mulligan <jmulligan@redhat.com>