Add clean in Makefile and use mountpoint instead of device

Using mountpoint instead of device is required to change the label
of a currently mounted filesystem.

debian.package/Makefile

@@ -24,3 +24,6 @@ db.crt db.key:
 
 db.cer:
 	openssl x509 -outform DER -in db.crt -out db.cer
+
+clean:
+	rm -rfv uefi-boot-metadata-collect-agent.deb dracut.conf db.key db.crt db.cer uefi-boot-metadata-collect-agent/boot
\ No newline at end of file

debian.package/uefi-boot-metadata-collect-agent/DEBIAN/postinst

@@ -5,8 +5,8 @@ ROOT_DEV=$(mount | grep -Po '^.+(?= on / )')
 
 efibootmgr --create --disk "$EFI_DEV" --label 'UEFI metadata-collect-agent' --loader /uefi-boot-metadata-collect-agent.efi
 
-e2label "$ROOT_DEV" "ROOT" || true
-btrfs filesystem label "$ROOT_DEV" "ROOT" || true
-reiserfstune -l "ROOT" "$ROOT_DEV" || true
-xfs_admin -L "ROOT" "$ROOT_DEV" || true
-cryptsetup config --label="ROOT" "$ROOT_DEV" || true
\ No newline at end of file
+e2label / "ROOT" || true
+btrfs filesystem label / "ROOT" || true
+reiserfstune -l "ROOT" / || true
+xfs_admin -L "ROOT" / || true
+cryptsetup config --label="ROOT" / || true
\ No newline at end of file