Use set -a/+a and docker env file formats

Closes https://git.autonomic.zone/coop-cloud/abra/issues/40.

abra

@@ -407,8 +407,11 @@ load_instance() {
 }
 
 load_instance_env() {
+  set -a
   # shellcheck disable=SC1090
   source "$ENV_FILE"
+  set +a
+
   if [ -z "$APP" ]; then
     error "APP not set, maybe $ENV_FILE is using an old format?"
   fi
@@ -513,10 +516,14 @@ sub_app_list (){
     FILE="${PARTS[-1]}"
     SERVER="${PARTS[-2]}"
     DOMAIN="${FILE%.env}"
+
     # shellcheck disable=SC1090
+    set -a
     APP="$(source "$ENV_FILE" && echo "$APP")"
     # shellcheck disable=SC1090
     APP_STACK_NAME="$(source "$ENV_FILE" && echo "$STACK_NAME")"
+    set +a
+
     if [ -z "$APP_STACK_NAME" ]; then
       APP_STACK_NAME="${DOMAIN//./_}"
     fi
@@ -1042,7 +1049,9 @@ abra() {
   # --env <env>
   if [ -n "$abra___env" ]; then
     # shellcheck disable=SC1090
+    set -a
     source "$abra___env" || error "Unable to load env from '$abra___env'"
+    set +a
   fi
 
   load_custom_commands