loop: add get_status method

Implement a `Loop.get_status` method, to get the properties of the
loop device, corresponding to LOOP_GET_STATUS64, and counterpart
to the existing `Loop.set_status` method. Use the new `get_status`
call in the `set_status` call, replacing the existing code that
does the same thing.
Add a basic test for the `get_status` method. Also fix an actual
leak, where the loop device was closed but the fd was not cleared
inside the test.

test/mod/test_loop.py

@@ -4,8 +4,6 @@
 
 import contextlib
 import os
-
-
 from tempfile import TemporaryDirectory
 
 import pytest
@@ -39,9 +37,15 @@ def test_basic(tempdir):
         f.flush()
         lo = ctl.loop_for_fd(f.fileno())
 
+        sb = os.fstat(f.fileno())
+
         assert lo
         assert lo.devname
 
+        info = lo.get_status()
+        assert info.lo_inode == sb.st_ino
+        assert info.lo_number == lo.minor
+
     finally:
         if lo:
             with contextlib.suppress(OSError):