backup: avoid deadlock on logging during restore
backup: avoid deadlock on logging during restore

When both threads and processes are used, logging module can deadlock.
Workaround this by re-initializating locks in logging module.
See https://bugs.python.org/issue6721 for details.
Revert this commit when the python issue is fixed (in the python version
used for backup restore).

marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client