[12.0][FIX] - report_py3o: run libreoffice in an isolated user installation

Bug when more than one conversion print is launched within the same libreoffice instance.

The standard behavior of libreoffice when a user open it while another instance is
running is to show a new window and throw an error if a new instance is forced within
the same user installation [see](https://bugs.documentfoundation.org/show_bug.cgi?id=37531).

This implies a bug in report_py3o module when we call libreoffice at the same time for
different documents.

To reproduce this bug:

**Case 1:**
1.  Simultaneously print two documents.

**Case 2:**
1.  Run print jobs using job_queue module
2.  Manually print another document

**Case 3:**
2.  Open libreoffice
3.  Print a py3o report

This PR creates a temporary user installation for each libreoffice conversion to bypass this limitation.

report_py3o/models/py3o_report.py

@@ -243,8 +243,12 @@ class Py3oReport(models.TransientModel):
     def _convert_single_report(self, result_path, model_instance, data):
         """Run a command to convert to our target format"""
         if not self.ir_actions_report_id.is_py3o_native_format:
+            with tempfile.TemporaryDirectory() as tmp_user_installation:
                 command = self._convert_single_report_cmd(
-                result_path, model_instance, data,
+                    result_path,
+                    model_instance,
+                    data,
+                    user_installation=tmp_user_installation,
                 )
                 logger.debug('Running command %s', command)
                 output = subprocess.check_output(
@@ -262,7 +266,9 @@ class Py3oReport(models.TransientModel):
         return result_path
 
     @api.multi
-    def _convert_single_report_cmd(self, result_path, model_instance, data):
+    def _convert_single_report_cmd(
+        self, result_path, model_instance, data, user_installation=None
+    ):
         """Return a command list suitable for use in subprocess.call"""
         lo_bin = self.ir_actions_report_id.lo_bin_path
         if not lo_bin:
@@ -270,13 +276,16 @@ class Py3oReport(models.TransientModel):
                 _("Libreoffice runtime not available. "
                   "Please contact your administrator.")
             )
-        return [
+        cmd = [
             lo_bin,
             '--headless',
             '--convert-to',
             self.ir_actions_report_id.py3o_filetype,
             result_path,
         ]
+        if user_installation:
+            cmd.append('-env:UserInstallation=file:%s' % user_installation)
+        return cmd
 
     @api.multi
     def _get_or_create_single_report(self, model_instance, data,