Samba POSIX Extensions automated testing

[Steve French]

With the migration to the new 'buildbot' (smb3.1.1 client test
automation) progressing, I have added some functional tests to the
Samba (with POSIX extensions enabled) test target.  We should add more
 xfstests to this test group as Samba server continues to improve its
support for POSIX extensions.   Here is the first test run on the new
infrastructure (server is Samba master branch, client is Linux cifs.ko
running on the 6.3 kernel):

http://smb311-linux-testing.southcentralus.cloudapp.azure.com/#/builders/11/builds/4

Some things that could help:
- support for clone (reflink) to Samba running on XFS, not just BTRFS
(reflink is helpful for more than just cloning files, various tests
require it)
- support for mknod/mkfifo
- support for ACLs and mode bits on the same share

-- 
Thanks,

Steve