Btrfs: add tests for btrfs_get_extent

I'm going to be removing hole extents in the near future so I wanted to make a
sanity test for btrfs_get_extent to make sure I don't break anything in the
meantime.  This patch just puts btrfs_get_extent through its paces by giving it
a completely unreasonable mapping to look at and make sure it is giving us back
maps that make sense.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 78041e3..1f62c1c 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1802,6 +1802,9 @@
 	if (ret)
 		goto out;
 	ret = btrfs_test_extent_io();
+	if (ret)
+		goto out;
+	ret = btrfs_test_inodes();
 out:
 	btrfs_destroy_test_fs();
 	return ret;