pacman: add --confirm option

--confirm cancels the effect of a previous --noconfirm.  This makes it
easier for scripts to default to --noconfirm but allowing users to
override it.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
pactest: allow specifying binary directories

Specifying binary directories rather than the binary itself allows
individual tests to easily specify a program other than pacman.

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
add pacman-db-upgrade test

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>