ibcli: use /var/cache/image-builder/store as default for --store

This commit follows a suggestion from Ondrej to add a better
default for `--store`: /var/cache/image-builder/store.

This is nice as it will give users automatic caching and makes
the container also nicer.

entrypoint.sh

@@ -6,7 +6,6 @@ set -e
 # see https://github.com/teamsbc/container-for-osbuild/blob/main/entrypoint.bash (thanks simon)
 # and https://github.com/osbuild/bootc-image-builder/blob/main/bib/internal/setup/setup.go#L21 (thanks ondrej,achilleas,colin)
 mkdir /run/osbuild
-mkdir /run/osbuild-store
 
 mount -t tmpfs tmpfs /run/osbuild
 
@@ -19,4 +18,4 @@ mount --bind /run/osbuild/osbuild /usr/bin/osbuild
 
 # XXX: make this nicer
 cd /output
-/usr/bin/image-builder --store=/store "$@"
+/usr/bin/image-builder "$@"