Michael Baudino authored Jun 18, 2020 and Bkg2k committed Aug 14, 2020

This commit started as an attempt to support logical partitions when
creating SHARE and OVERLAY partitions in S11share.

The rationale behind it was that NOOBS does not install OSs in a primary
partition (since it supports installing many OSs at once), but rather
creates an extended partition and then one logical partition inside it
per installed OS (this setup allows NOOBS to create more than 4
partitions, and thus to install as many OSs as they like on one disk).

Unfortunately, our convention is that SHARE should be the partition
immediately following the main one (the one mounted as /boot) and
OVERLAY should be the partition immediately following SHARE. Which was
an issue in the following scenario, occuring when installing Recalbox
via NOOBS (when it only creates the root partition):
1. NOOBS creates the following partitions (logical partitions are
always numbered 5+, 1-4 being reserved for primary/extended partitions):
  * `/dev/mmcblk0p1` → RECOVE...