Give temporary build directory a unique ID to allow for parallelism

src/freedombone-image

@@ -63,7 +63,8 @@ GENERIC_IMAGE_PASSWORD='freedombone'
 IMAGE_TYPE='beagleboneblack'
 CURR_DIR=$(pwd)
 CURR_USER="$USER"
-TEMPBUILD_DIR=~/.tmp_${PROJECT_NAME}_build
+UNIQUE_ID=$(openssl rand -base64 32 | tr -dc A-Za-z0-9 | head -c 10 ; echo -n '')
+TEMPBUILD_DIR=~/.tmp_${PROJECT_NAME}_build_${UNIQUE_ID}
 VMDEBOOTSTRAP_REPO=git://git.liw.fi/vmdebootstrap
 VMDEBOOTSTRAP_VERSION=0.8
 MAKEFILE=${PROJECT_NAME}-image-makefile