Upgraded to php7.0, now ssh updates don't work
I updated my server from Ubuntu 15.10 to Ubuntu 16.04, and one of the things that updated was PHP. After the upgrade, doing plugin updates over ssh don't work any more.
At first it was prompting for FTP login credentials until I installed php-ssh2 (which cautions that it's based on a git snapshot). Now when I try to upgrade a plugin, it says
An error occurred while updating WP to Twitter: Unable to locate WordPress Content directory (wp-content).
And in /var/log/apache2/error.log:
[Sun Jun 12 11:01:10.969931 2016] [:error] [pid 5545] [client 192.168.1.11:65278] PHP Warning: file_put_contents(): Unable to open ssh2.sftp://Resource id #81/.maintenance on remote host in /home/blog/wordpress/wp-admin/includes/class-wp-filesystem-ssh2.php on line 252, referer: http://xxxx.com/wp-admin/update-core.php?action=do-plugin-upgrade
[Sun Jun 12 11:01:10.970772 2016] [:error] [pid 5545] [client 192.168.1.11:65278] PHP Warning: file_put_contents(ssh2.sftp://Resource id #81/.maintenance): failed to open stream: operation failed in /home/blog/wordpress/wp-admin/includes/class-wp-filesystem-ssh2.php on line 252, referer: http://xxxx.com/wp-admin/update-core.php?action=do-plugin-upgrade
Am I missing a package, or a configuration item, or what?