Add better test coverage for #6647

[vburenin]

User Statement:
#6647 is not covered by direct test, however, that logic runs every time VCH boots or gets new IP address via DHCP. The test coverage is not that trivial. As functional test requirement two things needs to be tested, the trace path as well as the content of bridge.out routing table on VCH.

Acceptance Criteria:
bridge.out contains a network route to the network where default VCH gateway is.
default gateway doesn't appear in trace path when container traces path to the IP address that in the same network where default VCH gateway is. (use different IP from default gateway).

[zjs]

Sending back for estimation by the team.