Contrail: Fix logrotate configuration (use copytruncate)

Truncate the original log file to zero size in place after creating a
copy, instead of moving the old log file and optionally creating a new
one.

Change-Id: I60a8632199728ea5667f34539c987985aaba0a97
(cherry picked from commit 05324ed98329804d4f30201d28280ab251f82343)