cros_workon_make: simplify common variables

We duplicate a few variables in a bunch of places.  Unify all that near
the top so the resulting code is simpler.

BUG=chromium:311351
TEST=`cros_workon_make --board x86-generic crash-reporter` still works
TEST=`cros_workon_make --board x86-generic --test crash-reporter` still works

Change-Id: I1e9dce0b5c2843e305b30e1c53240197f76ad8f5
Reviewed-on: https://chromium-review.googlesource.com/174676
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed