openstreetmap syncing should use less memory

There is no reason for osm2pgsql to use so much memory, in fact it is a
liability since it may fail for whatever reason. The probability of the
above is increased due to the way osm2pgsql relies on VM management
While at it log the last run at /tmp/osmosis.log

Change-Id: Ibbd2abeadb670422eca7173783134893945fe708