build-setup: initialise PROXY variable

This is to avoid instance where no PROXY env exists and set -e catches
the unbound variable.

Signed-off-by: Chris Smart <distroguy@gmail.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/build-setup.sh b/build-setup.sh
index d0a6fc2..91778f9 100755
--- a/build-setup.sh
+++ b/build-setup.sh
@@ -15,6 +15,7 @@
 distro=${distro:-ubuntu}
 WORKSPACE=${WORKSPACE:-${HOME}/${RANDOM}${RANDOM}}
 http_proxy=${http_proxy:-}
+PROXY=""
 
 # Timestamp for job
 echo "Build started, $(date)"