get_current db issue

[wtgee]

Since #414 was merged there is a frequent problem that when the weather record is being updated it is no longer available in the collection, causing weather safety to fail and parking the unit. It seems like the insert_current is taking a non-negligible amount of time to update.

However, on PAN001 I am getting a failure after during the weather check after every move past the pointing state although the checks before that work fine, so it doesn't seem to necessarily be a timing issue.

Will do more debugging.

[wtgee]

Figured this out. I added in an option to clear out the current collection whenever a new database connection is made. This is fine for peas_shell and pocs_shell, which are long running, but the plot_weather script (for example) run every 5 minutes from cron so is creating a new process and hence new db connection each time. It clears the value whenever this happens and suddenly there is no record for weather in the current collection.

Will remove the clearing.