In case when L3 agent is running in dvr_snat mode on compute node,
it is like that e.g. in some of the gate jobs, it may happen that
same router is scheduled to be in standby mode on compute node and
on same compute node there is instance connected to it.
So in such case metadata proxy needs to be spawned in router namespace
even if it is in standby mode.
Change-Id: Id646ab2c184c7a1d5ac38286a0162dd37d72df6e
Closes-Bug: #1817956
Closes-Bug: #1606741
(cherry picked from commit 6ae228cc2e)