rados/singleton: use xfs instead

Signed-off-by: Samuel Just <sjust@redhat.com>

diff --git a/suites/rados/singleton/fs/btrfs.yaml b/suites/rados/singleton/fs/btrfs.yaml
deleted file mode 120000 (symlink)
index 10d0c3f..0000000
--- a/suites/rados/singleton/fs/btrfs.yaml
+++ /dev/null
@@ -1 +0,0 @@
-../../../../fs/btrfs.yaml
\ No newline at end of file

diff --git a/suites/rados/singleton/fs/xfs.yaml b/suites/rados/singleton/fs/xfs.yaml
new file mode 120000 (symlink)
index 0000000..4c28d73
--- /dev/null
+++ b/suites/rados/singleton/fs/xfs.yaml
@@ -0,0 +1 @@
+../../../../fs/xfs.yaml
\ No newline at end of file