add sim destroy_pool_w_filesystem test
add sim destroy_pool_w_filesystem test

Unlike blockdevs, if there's a filesystem created from the pool then
destroy_pool() should fail.

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

stratis-storage/stratisd,mulkieran/stratisd,trgill/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,trgill/stratisd,mulkieran/stratisd