refactor(partitioning): extract VG name to defaults variable

roles/partitioning/defaults/main.yml

@@ -6,6 +6,7 @@ partitioning_efi_size_mib: 512
 partitioning_efi_start_mib: 1
 partitioning_efi_end_mib: "{{ (partitioning_efi_start_mib | int) + (partitioning_efi_size_mib | int) }}"
 partitioning_boot_size_mib: 1024
+partitioning_vg_name: sys
 partitioning_use_full_disk: true
 partitioning_separate_boot: >-
   {{