Repeat to umount filesystem when exception occurs

Sometimes umount doesn't have much time to finish and failed with
error 'target is busy', but this is not an actual error in some cases
and the operation should be repeated again with some timeout.

This solves the issue and raise actual exception only after several
tries with timeout.

Closes-Bug: #2004492
Change-Id: I069af85b52e20e9fd688f9ae07e66beb2179f3e1
Signed-off-by: Maksim Malchuk <maksim.malchuk@gmail.com>

diskimage_builder/block_device/level3/mount.py

@@ -15,6 +15,7 @@
 import functools
 import logging
 import os
+import time
 
 from diskimage_builder.block_device.exception \
     import BlockDeviceSetupException
@@ -109,7 +110,21 @@ class MountPointNode(NodeBase):
         if self.state['filesys'][self.base]['fstype'] != 'vfat':
             exec_sudo(["fstrim", "--verbose",
                        self.state['mount'][self.mount_point]['path']])
-        exec_sudo(["umount", self.state['mount'][self.mount_point]['path']])
+        # Even 'fstrim' call sometimes don't solve the issue with 'busy'
+        # filesystem, so we need to catch the exception and repeat unount.
+        mount_point = self.state['mount'][self.mount_point]['path']
+        catch = None
+        for try_cnt in range(10, 1, -1):
+            try:
+                exec_sudo(["umount", mount_point])
+                return
+            except BlockDeviceSetupException as e:
+                catch = e
+                logger.error("umount failed (%s)", e.output.strip())
+                time.sleep(3)
+
+        logger.debug("Gave up trying to umount [%s]", mount_point)
+        raise catch
 
     def delete(self):
         self.umount()