Ensure HOME is set for post hook as root

Even though we are running as a login shell, the HOME is
not being set and hence neither is GOCACHE which is required
for golang 1.12 and beyond.

Signed-off-by: Mark D Horn <mark.d.horn@intel.com>

scripts/developer-image-post.sh

@@ -3,6 +3,7 @@
 DESTDIR=$1
 SAVE_DIR=$(pwd)
 TEMP_INST=$(mktemp -d)
+export HOME=$(getent passwd $(id -un) |& awk -F: '{print $(NF-1)}')
 git clone . ${TEMP_INST}
 cd ${TEMP_INST}
 make install DESTDIR=${DESTDIR}