udp2log: let daemon recreate files after logrotate

When rotating a file, logrotate will recreate a file that belong to
root:root then adjust the ownership to whatever the previous file had.

On labs, the logs directory is a NFS mount which does not allow a file
belonging to root to have ownership changed (root_squash is enabled by
default). Hence logrotate fails to change the ownership back to
udp2log:udp2log and the daemon is unable to write to the root owned
file.

I believe the udplog daemon is able to create the file whenever it does
not exist.  On initial startup with an empty logs directory,  the daemon
does create the files as it receives the UDP packets.

bug: 47980
Change-Id: I048c6914b6bf7c93cc7d98658391ba90d388ff4b
Merge "udp2log: let daemon recreate files after logrotate" into production