util: Set program_name for windows correctly.

util: Set program_name for windows correctly.

Windows path uses backward slashes. Also, the executable name
has a .exe extension in it. While creating log files, we use
the program name to create log file names. It feels a little odd
to have log file names like ovsdb-server.exe.log etc. Using
_splitpath_s() is a way to have same log file names on both
windows and linux platforms.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>