test/hello_world: Properly report P9MAMBO path
test/hello_world: Properly report P9MAMBO path

In the P9 hello script we look for $P9MAMBO_BINARY, but then if we don't
find it we print a message using $MAMBO_BINARY, which is confusing:

  $ set -x P9MAMBO_BINARY run/p9/run_cmdline
  $ ./test/hello_world/run_mambo_p9_hello_world.sh
  Could not find executable P9MAMBO_BINARY (/opt/ibm/systemsim-p9//).

Fix it so the right thing is printed:

  Could not find executable P9MAMBO_BINARY (/opt/ibm/systemsim-p9//run/p9/run_cmdline).

Signed-off-by: Michael Ellerman <864f124608374e06e4da1fa5d2e47ed839b95411@ellerman.id.au>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

shenki/skiboot,legoater/skiboot,legoater/skiboot,legoater/skiboot,open-power/skiboot,qemu/skiboot,qemu/skiboot,qemu/skiboot,qemu/skiboot,open-power/skiboot,legoater/skiboot,legoater/skiboot,mikey/skiboot,qemu/skiboot,stewart-ibm/skiboot,open-power/skiboot,shenki/skiboot,stewart-ibm/skiboot,open-power/skiboot,shenki/skiboot,mikey/skiboot,mikey/skiboot,stewart-ibm/skiboot,shenki/skiboot,open-power/skiboot,shenki/skiboot