provisioning does not cleanup mounted resources

[igalic]

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so re-running a provisioning, leads to:

# ioc -d debug provision webproxy
/iocage/pkg/12/cache mounted to running jail webproxy
/iocage/jails/webproxy/fstab written
Adding line to fstab: /usr/local/etc/puppet/environments        /iocage/jails/webproxy/root/usr/local/etc/puppet/environments   nullfs  ro      0       0
auto-mount /iocage/jails/webproxy/root/usr/local/etc/puppet/environments
Command exited with 1: /sbin/mount -o ro -t nullfs /usr/local/etc/puppet/environments /iocage/jails/webproxy/root/usr/local/etc/puppet/environments
    mount_nullfs: /iocage/jails/webproxy/root/usr/local/etc/puppet/environments: Resource deadlock avoided
Command exited with 1

[igalic]

fixed with #725.