Fix erroneous usage of 'qubes' module

On the client side it should use only 'qubesadmin'. In practice, those
few are trivial to replace:
 - get_disk_usage() is also available in shutil (as disk_usage())
 - BackupCancelledError should be used from qubesadmin.exc anyway (there
   was also a typo)

Remove also test-packages/qubes to let pylint detect such issues in the
future.

QubesOS/qubes-issues#5403

qubesmanager/backup.py

@@ -23,7 +23,6 @@
 import signal
 from qubesadmin import exc
 from qubesadmin import utils as admin_utils
-from qubes.storage.file import get_disk_usage
 
 from PyQt5 import QtCore, QtWidgets  # pylint: disable=import-error
 from . import ui_backupdlg  # pylint: disable=no-name-in-module
@@ -35,6 +34,7 @@ from . import utils
 import grp
 import pwd
 import os
+import shutil
 
 
 # pylint: disable=too-few-public-methods
@@ -202,7 +202,7 @@ class BackupVMsWindow(ui_backupdlg.Ui_Backup, QtWidgets.QWizard):
             if vm.qid == 0:
                 local_user = grp.getgrnam('qubes').gr_mem[0]
                 home_dir = pwd.getpwnam(local_user).pw_dir
-                self.size = get_disk_usage(home_dir)
+                self.size = shutil.disk_usage(home_dir)[1]
             else:
                 self.size = vm.get_disk_utilization()
             super(BackupVMsWindow.VmListItem, self).__init__(

qubesmanager/restore.py

@@ -26,8 +26,6 @@ import os.path
 import logging
 import logging.handlers
 
-from qubes import backup
-
 from . import ui_restoredlg  # pylint: disable=no-name-in-module
 from . import multiselectwidget
 from . import backup_utils
@@ -53,7 +51,7 @@ class RestoreThread(QtCore.QThread):
         try:
             self.backup_restore.restore_do(self.vms_to_restore)
 
-        except backup.BackupCanceledError as ex:
+        except exc.BackupCancelledError as ex:
             self.canceled = True
             err_msg.append(str(ex))
         except Exception as ex:  # pylint: disable=broad-except

test-packages/qubes/backup/__init__.py

@@ -1,5 +0,0 @@
-class BackupCanceledError(BaseException):
-
-    tmpdir = None
-
-    pass

test-packages/qubes/storage/__init__.py

@@ -1 +0,0 @@
-pass

test-packages/qubes/storage/file.py

@@ -1,2 +0,0 @@
-def get_disk_usage(*args):
-    return 0

test-packages/qubesadmin/exc.py

@@ -13,3 +13,6 @@ class QubesPropertyAccessError(BaseException):
 
 class QubesDaemonNoResponseError(BaseException):
     pass
+
+class BackupCancelledError(BaseException):
+    pass