io_openhab2 driver does not support influxdb as persistence backend

[lausitzer]

First of all, the current openhab2 driver works like a charm for me. Thanks to its developers!

The current implementation is limited to rrd4j as persistence backend. I dont know why, its hard coded in the url. From my point of view there is no reason for this limitation. Openhab should encapsulte the different persistence providers it supports. When I removed the servicename=rrd4j param from the url and removed the ms-portion from starttime it works with influxdb out of the box.
Also changed path from /rest/persistence/{ohItem} to /rest/persistence/items/{ohItem} for current Openhab 2.2.0