Do not erase a datacenter in case of harvesting failure

[jschaeff]

This is maybe a dup of #66 but it happens from time to time that a datacenter will not serve correctly the data on harvesting from the central system.

There should be a protection mechanism to prevent a datacenter from disapearing in such cases.

[jschaeff]

@javiquinte I think this issue is fixed. Could you please tell @jppzanetti which release he should deploy ?

[jppzanetti]

We are running what I thought was the latest release, v1.2.3.post2

[javiquinte]

Hi @jppzanetti !
I've deployed at GEOFON a new release (v1.2.3.post3). Please, let me run it for a couple of days to see that everything works correctly and after that feel free to deploy it whenever you want.
I've included more safety measures against weird cases that could happen while harvesting and updating.