Rework how lvm.conf is patched

[simondeziel]

Another attempt at fixing canonical/lxd#14341

This changes how lvm.conf is patched to be done at build time rather than at daemon.start time. This implies that now, executables are using /snap/lxd/current instead of /snap/lxd/${rev}. /etc/lvm/profile files are now included in the snap. It's unclear if they are used or not but they are so small (11KiB) that it doesn't hurt to ship them.

Lastly, the daemon visible /etc/lvm dir now contains 2 symlinks pointing to the read-only snap mount while still allowing the creation of the /etc/lvm/archive and /etc/lvm/backup directories backed by the tmpfs /etc:

# LD_LIBRARY_PATH=/snap/lxd/current/lib/:/snap/lxd/current/lib/x86_64-linux-gnu/:/snap/lxd/current/zfs-2.2/lib PATH=/snap/lxd/current/zfs-2.2/bin:/snap/lxd/current/bin:$PATH nsenter --mount=/run/snapd/ns/lxd.mnt -- ls -l /etc/lvm
total 0
drwx------ 2 root root 1860 Nov 14 19:54 archive
drwx------ 2 root root   40 Nov 14 19:54 backup
lrwxrwxrwx 1 root root   29 Nov 14 19:43 lvm.conf -> /snap/lxd/x1/etc/lvm/lvm.conf
lrwxrwxrwx 1 root root   28 Nov 14 19:43 profile -> /snap/lxd/x1/etc/lvm/profile

[simondeziel]

@tomponline when you get a chance, I'm eager to see if that will improve the situation with lvm slowness with latest/edge :)