Fix AttributeError caused by updated pymongo version

AttributeError: 'Cursor' object has no attribute 'count' is fixed.

Change-Id: Id1b9133376d5a7dcb3998c623163bb57dd5c534b
Signed-off-by: Gulsum Atici <gulsum.atici@canonical.com>
diff --git a/osm_common/dbmongo.py b/osm_common/dbmongo.py
index f5c4d30..c9b384b 100644
--- a/osm_common/dbmongo.py
+++ b/osm_common/dbmongo.py
@@ -308,8 +308,8 @@
                 collection = self.db[table]
                 if not (fail_on_empty and fail_on_more):
                     return collection.find_one(db_filter)
-                rows = collection.find(db_filter)
-            if rows.count() == 0:
+                rows = list(collection.find(db_filter))
+            if len(rows) == 0:
                 if fail_on_empty:
                     raise DbException(
                         "Not found any {} with filter='{}'".format(
@@ -317,8 +317,9 @@
                         ),
                         HTTPStatus.NOT_FOUND,
                     )
+
                 return None
-            elif rows.count() > 1:
+            elif len(rows) > 1:
                 if fail_on_more:
                     raise DbException(
                         "Found more than one {} with filter='{}'".format(