Handle log stuff in a more robust manner bootstrap script

hack/bootstrap_tfw_dev.sh

@@ -6,7 +6,11 @@ BASEIMAGE=baseimage-${TFW_POSTFIX}
 BACKEND=test-${TFW_POSTFIX}
 FRONTEND=frontend-${TFW_POSTFIX}
 LOGFILE=/tmp/bootstrap_tfw.log
-trap 'echo && echo "Error! Showing logs at $LOGFILE:" && cat $LOGFILE' ERR
+
+showlog() { echo && echo "Error! Showing logs:" && cat $LOGFILE; }
+cleanlog() { rm $LOGFILE; }
+trap showlog ERR
+trap cleanlog EXIT
 
 : > $LOGFILE
 echo -n "Cloning TFW repositories... "
@@ -27,4 +31,3 @@ wait
 echo "Done!"
 echo 
 echo "You can start TFW by executing the ${BACKEND}/hack/tfw_magic_start.sh script."
-rm $LOGFILE