partman-efi should follow partman-auto/disk to reuse the ESP.

[Shih-Yuan Lee]

   Current implementation in partman-efi/fstab.d/efi is to find the
   first EFI System Partition (abbr. ESP) to use when we provided
   some kind of partman-auto/expert_recipe.

   However if the system has more than two ESPs, partman-efi will still
   use the first ESP it found even when we specify what we want in
   partman-auto/disk.

   For example, when the system has /dev/nvme0n1 and /dev/sda and we
   specified partman-auto/disk and partman-auto/expert_recipe as the following.

       d-i partman-auto/disk string /dev/sda
       d-i partman-auto/expert_recipe string \
                                             \
         ubuntu :: \
             100 150 200 free \
             $iflabel{ gpt } \
             $reusemethod{ } \
             method{ efi } \
             format{ } . \
                                             \
             500 10000 4000000 ext4 \
             $primary{ } \
             method{ format } \
             format{ } \
             use_filesystem{ } \
             filesystem{ ext4 } \
             mountpoint{ / } . \
                                             \
             105% 150% 200% linux-swap \
             method{ swap } \
             format{ } \
             .

   If there is already another Linux system installed in /dev/nvme0n1,
   partman-efi will reuse /dev/nvme0n1p1 and mount it at
   /target/boot/efi instead of reusing /dev/sda1 that we specify in
   partman-auto/disk.

   This should not be the behavior that we expected it will be.