Enable sysroot.bootprefix by default

I've been testing this in various places and not seen any fallout,
so let's finally enable this by default and have the situation where
`/boot` is on the root `/` filesystem work out of the box.

src/libostree/ostree-repo.c

@@ -3346,7 +3346,7 @@ reload_sysroot_config (OstreeRepo *self, GCancellable *cancellable, GError **err
       g_hash_table_replace (self->bls_append_values, key, value);
     }
 
-  if (!ot_keyfile_get_boolean_with_default (self->config, "sysroot", "bootprefix", FALSE,
+  if (!ot_keyfile_get_boolean_with_default (self->config, "sysroot", "bootprefix", TRUE,
                                             &self->enable_bootprefix, error))
     return FALSE;
 

tests/test-admin-deploy-bootprefix.sh

@@ -25,7 +25,7 @@ set -euo pipefail
 setup_os_repository "archive" "syslinux"
 
 ${CMD_PREFIX} ostree --repo=sysroot/ostree/repo pull-local --remote=testos testos-repo testos/buildmain/x86_64-runtime
-${CMD_PREFIX} ostree --repo=sysroot/ostree/repo config set sysroot.bootprefix 'true'
+# sysroot.bootprefix is on by default now
 ${CMD_PREFIX} ostree admin deploy --karg=root=LABEL=root --os=testos testos:testos/buildmain/x86_64-runtime
 assert_file_has_content_literal sysroot/boot/loader/entries/ostree-1-testos.conf 'linux /boot/ostree/testos-'
 assert_file_has_content_literal sysroot/boot/loader/entries/ostree-1-testos.conf 'initrd /boot/ostree/testos-'