vfs_fake_dfq: add more mocking options

vfs_fake_dfq: add more mocking options

Add support for mocking FS user/group quotas (default quota and
quota flags).

Make the default block size 4096 instead of 0. This
turns the default into "no quota" instead of "punt to
lower VFS module" (that is, if the mock module is asked
to retrieve quota of a user/group/default for which there
is no config).

Add support for ENOSYS error

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11937

Signed-off-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>