Use sqlite3.backup

The next version 3.7 (normally) of Python should support backup in sqlite3.
So we could stop using sqlitebck for the test.

https://github.com/python/cpython/commit/d7aed4102d2a40c74553240c7f03585624d27aea

assigned to @ced

added trytond type::feature + 1 deleted label

added 1 deleted label and removed 1 deleted label

review44131002 updated at https://codereview.tryton.org/44131002/#ps1

New review53341002 at https://codereview.tryton.org/53341002/#ps1

review44131002 updated at https://codereview.tryton.org/44131002/#ps20001

New changeset 085c43f10fc4 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account/rev/085c43f10fc4

added 1 deleted label and removed 1 deleted label

closed

New changeset 65d480bacb74 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_asset/rev/65d480bacb74

New changeset 6bf4b5bead0c by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_be/rev/6bf4b5bead0c

New changeset 5cbf0f3748b3 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_credit_limit/rev/5cbf0f3748b3

New changeset 449e7a3504f0 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_de_skr03/rev/449e7a3504f0

New changeset 55d3bf4b1e73 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_deposit/rev/55d3bf4b1e73

New changeset 43ff9bf2e9af by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_dunning/rev/43ff9bf2e9af

New changeset b93e3889229e by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_dunning_email/rev/b93e3889229e

New changeset 81e9428acc3d by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/cookiecutter/rev/81e9428acc3d

New changeset 4c1ce56e2b1d by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_dunning_fee/rev/4c1ce56e2b1d

New changeset c9e59db2b518 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_dunning_letter/rev/c9e59db2b518

New changeset 7c5f163724a9 by Cédric Krier in branch 'default':
Use sqlite3.backup when available
https://hg.tryton.org/modules/account_es/rev/7c5f163724a9