Avoid variable named 'stat'

Avoid variable named 'stat'

Using a variable named 'stat' clashes with the system function
'stat()' causing compiler warnings on some platforms

cc1: warnings being treated as errors
../../src/qemu/qemu_monitor_text.c: In function 'parseMemoryStat':
../../src/qemu/qemu_monitor_text.c:604: error: declaration of 'stat' shadows a global declaration [-Wshadow]
/usr/include/sys/stat.h:455: error: shadowed declaration is here [-Wshadow]

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>