Previously o_tmpfile support was detected by checking the
kernel version as it was officially introduced in XFS in 3.15.
The problem is that RHEL has backported the support to at least
RHEL 7.6 but the kernel version is not updated.
This patch changes o_tmpfile is detected by actually attempting to
open a file with the O_TMPFILE flag and keeps the information cached
in DiskFileManager so that the check only happens once while process
is running.
Change-Id: I3599e2ab257bcd99467aee83b747939afac639d8
0668731839