Update poudriere to *always* copy in the host's emulator on a bulk run.

Move check_emulation/need_emulation into common.sh so it can be invoked and
handled from anywhere (bulk.sh and jail.sh)

Add arguments to check_emulation for jail arch and host arch to compare and
use as arguments to find the emulator

Globally defined BINMISCCTL and EMULATOR for these purposes.

Tested on amd64 with a mips32/64 and armv632 jail.