Update the datastore lock code

[janette]

Reminders

• There is test for the issue.
• Coding standards checked.
• Review docs.getdkan.com (or in /docs) to see if it still covers the scope of the PR and update if needed.

[janette]

lock is stored in a global lock variable, requesting a new lock will extend the expiration of the lock and return true. So to test a failed lock we need it to be called from a separate process.

to test we need a server to request a url
https://api.drupal.org/api/drupal/modules%21simpletest%21tests%21lock.test/function/LockFunctionalTest%3A%3AtestLockAcquire/7.x

hypothesis: use a drush command to acquire a lock, run a second drush command to also acquire the lock

Create a new ticket.