Fix compatibility with procps 4.

Negative UIDs are no longer allowed.  Use a very high one instead.

Taken from upstream:

  https://github.com/ganeti/ganeti/commit/9cd67e6a81c66ed326d68ea8c3241d14eea6550b

diff --git a/test/py/ganeti.uidpool_unittest.py b/test/py/ganeti.uidpool_unittest.py
index b2f5bc5cf2..2d9227cbf5 100755
--- a/test/py/ganeti.uidpool_unittest.py
+++ b/test/py/ganeti.uidpool_unittest.py
@@ -106,23 +106,24 @@ def testRequestUnusedUid(self):
 
     # Check with a single, known unused user-id
     #
-    # We use "-1" here, which is not a valid user-id, so it's
-    # guaranteed that it's unused.
-    uid = uidpool.RequestUnusedUid(set([-1]))
-    self.assertEqualValues(uid.GetUid(), -1)
+    # We use 2^30+42 here, which is a valid UID, but unlikely to be used on
+    # most systems (even as a subuid).
+    free_uid = 2**30 + 42
+    uid = uidpool.RequestUnusedUid(set([free_uid]))
+    self.assertEqualValues(uid.GetUid(), free_uid)
 
     # Check uid-pool exhaustion
     #
-    # uid "-1" is locked now, so RequestUnusedUid is expected to fail
+    # free_uid is locked now, so RequestUnusedUid is expected to fail
     self.assertRaises(errors.LockError,
                       uidpool.RequestUnusedUid,
-                      set([-1]))
+                      set([free_uid]))
 
     # Check unlocking
     uid.Unlock()
     # After unlocking, "-1" should be available again
-    uid = uidpool.RequestUnusedUid(set([-1]))
-    self.assertEqualValues(uid.GetUid(), -1)
+    uid = uidpool.RequestUnusedUid(set([free_uid]))
+    self.assertEqualValues(uid.GetUid(), free_uid)
 
 
 if __name__ == "__main__":
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<tr><td><span title='2023-05-31 17:23:21 +0200'>2023-05-31</span></td><td><a href='/guix/commit/po/packages/hu.po?id=8e9e6a6482f3ba98d1cdcad344ee488e8751fee7'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix-cookbook.texi (Top): Mention Slovak.
</span></span></td><td>Florian Pelz</td></tr>
<tr><td><span title='2023-03-07 21:14:57 +0100'>2023-03-07</span></td><td><a href='/guix/commit/po/packages/hu.po?id=d333958763b0840c4cd895601b079b68358a6a46'>nls: Update translations.</a></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-12-04 22:25:23 +0100'>2022-12-04</span></td><td><a href='/guix/commit/po/packages/hu.po?id=2e75b328b6bbdadbffe5b643a4891b5026a0defd'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/packages/vi.po: New file.
po/packages/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-11-04 10:56:38 +0100'>2022-11-04</span></td><td><a href='/guix/commit/po/packages/hu.po?id=a65ce9dd500460af4f97e7398fb35dd817f4c677'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>* po/guix/lt.po: New file.
* po/guix/LINGUAS: Add lt.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-10-06 08:20:20 +0200'>2022-10-06</span></td><td><a href='/guix/commit/po/packages/hu.po?id=70fc8f6d619ce9f16a8cc0bbb10a011bd3a9997a'>nls: Update translations.</a></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-09-04 16:52:02 +0200'>2022-09-04</span></td><td><a href='/guix/commit/po/packages/hu.po?id=77e3042aef6d8e519d016555464e466399318b4f'>nls: Update translations.</a></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-08-10 23:32:24 +0200'>2022-08-10</span></td><td><a href='/guix/commit/po/packages/hu.po?id=aacbe59fbceb8a93ecb68fed8581dfdd70dafc11'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/guix/bn.po: New file.
po/guix/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>