Put root file system value in a variable

It is passed to bootstrap.sh to allow for defining it in a *single*
location.

bootstrap.sh

@@ -10,8 +10,8 @@ export DEBIAN_FRONTEND
 apt-get update
 apt-get install debootstrap -q -y
 
-rootfs=$PWD/rootfs
 suite=$1
+rootfs=$2
 
 debootstrap \
     --force-check-gpg \

build.sh

@@ -6,15 +6,16 @@
 
 MIGRATED_IMAGE=$CI_REGISTRY_IMAGE/debian-$DEBIAN_VERSION/migrated
 SUITE=$1
+ROOTFS=rootfs
 
-rm -rf rootfs || true
+rm -rf $ROOTFS || true
 
 docker pull $MIGRATED_IMAGE
 docker run --rm \
        --cap-add SYS_ADMIN \
        --volume $PWD:/devuan \
        --workdir /devuan \
-       $MIGRATED_IMAGE ./bootstrap.sh $SUITE
+       $MIGRATED_IMAGE ./bootstrap.sh $SUITE $ROOTFS
 
 IMAGE=$CI_REGISTRY_IMAGE
 STAMP=$(date +%F)