Support for install-to-filesystem --replace=alongside

[cgwalters]

install: Trim bind mount information

I'm seeing this appear when targeting from a container image.

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Support for install-to-filesystem --replace=alongside

I was trying to be really ambitious in #78
for the full "takeover" path. This is a much much simpler variant
where we just:

• Blow away and reinitialize the /boot and /boot/efi partitions
• Write inside the existing filesystem, leaving the OS running

Then when we reboot, we'll just need to clean up the old OS
state (or optionally leave it).

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[cgwalters]

Demo:

$ podman run --privileged -v /:/target --pid=host --net=none --security-opt label=type:install_t quay.io/cgwalters/ostest bootc install-to-filesystem --replace=alongside /target

[cgwalters]

Notes to myself, script for testing this:

#!/bin/bash
set -xeuo pipefail
install /run/hostsrv/src/github/containers/bootc/target/release/bootc /usr/bin
podman run --rm --privileged --env BOOTC_BOOTLOADER_DEBUG=1 --pid=host -v /usr/bin/bootc:/usr/bin/bootc -v /:/target --security-opt label=type:install_t registry.gitlab.com/centos/cloud/sagano/fedora-boot-tier-0-dev:38 bootc install-to-filesystem --target-no-signature-verification --karg=console=ttyS0,115200n8 --replace=alongside /target

Note that we effectively bind mount in /usr/bin/bootc from the host devenv all the way into the container for faster iteration.