d/swtpm-tools postinst: avoid trying to create/chown in non-configure steps

configure steps should be limited to get only executed on, well
configuration, so check for that and do nothing in the remaining
commands [0] the postinst can be called with.

[0]: https://www.debian.org/doc/debian-policy/ch-maintainerscripts.html#summary-of-ways-maintainer-scripts-are-called

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
1 file changed