Rename LOGNAME to LOGFILENAME.

LOGNAME has historically been used for the username.  Using it for
the logfile name causes confusion.  For example, Python's
getpass.getuser() will return the value of LOGNAME.

Change-Id: I3f569d54f93c4898654fddb91f3b569831e75a2c
Merge "Rename LOGNAME to LOGFILENAME."