[fpv/tooling] add FPV class extension in dvsim

Follow Michael's suggestion in PR 1854. This PR adds FPV python file
extension to support running FPV on dvsim
This PR assumes FPV result will be parsed as a hjson format

Signed-off-by: Cindy Chen <chencindy@google.com>
diff --git a/util/dvsim/OneShotCfg.py b/util/dvsim/OneShotCfg.py
index 6ff46b4..578ba47 100644
--- a/util/dvsim/OneShotCfg.py
+++ b/util/dvsim/OneShotCfg.py
@@ -74,7 +74,7 @@
         self.links = {}
         self.build_list = []
         self.deploy = []
-
+        self.cov = args.cov
         # Parse the cfg_file file tree
         self.parse_flow_cfg(flow_cfg_file)
         self._post_parse_flow_cfg()