[BUG] Increase wait state timing after asking statistics

[JeromeGalan]

Describe the bug
First statistics are never received with some setups.
Linked to : Luos-io/luos_engine#116

How to reproduce the bug
On first statistic asking.

Additional context
def luos_statistics(self):
self._push_value('luos_statistics', "")
time.sleep(0.3) <--- this value should be greater

[fleborne]

I encountered this problem too.

Since I already have an open PR to improve statistics management, I added a commit that solves the current issue: 745becf