Improve TFWDEV detection logic to allow use of set -u

hack/bootstrap_tfw_dev.sh

@@ -1,10 +1,11 @@
 #!/usr/bin/env bash
-set -e
+set -eu
 set -o pipefail
 set -o errtrace
 shopt -s expand_aliases
 [ "$(uname)" == "Darwin" ] && alias sed="gsed" || :
 
+TFWDEV="${TFWDEV:-0}"
 TFW_POSTFIX=tutorial-framework
 BASEIMAGE=baseimage-${TFW_POSTFIX}
 TEST=test-${TFW_POSTFIX}
@@ -19,7 +20,7 @@ run()
 
     clone_repos
     install_frontend_deps
-    if [ -z "$TFWDEV" ]; then
+    if [ "$TFWDEV" == "0" ]; then
         LATESTTAG="$(fetch_latest_tag)"
         LATESTTAG=$LATESTTAG pin_latest_baseimage
         LATESTTAG=$LATESTTAG build_latest_baseimage

hack/oneline_install.sh

@@ -1 +1 @@
-URL=https://git.io/vxBfj SHA=e72bc2836448c4ab0171d637b459546f927ae7ec63cafa2bf4596f50eaaa0aec bash -c 'cmd="$(curl -fsSL $URL)" && [ $(echo "$cmd" | sha256sum | cut -d " " -f1) == $SHA ] && echo "$cmd" | bash || echo Checksum mismatch!'
+URL=https://git.io/vxBfj SHA=40cf2fec4e9d378dd8a4f049fd6ba7b7c415bf699e0a6e329ec8e3cf3f5d383c bash -c 'cmd="$(curl -fsSL $URL)" && [ $(echo "$cmd" | sha256sum | cut -d " " -f1) == $SHA ] && echo "$cmd" | bash || echo Checksum mismatch!'