This is to address the need that openvswitch starting with 2.13 now
depends on libunwind for handling SIGSEGV (upstream commit e2ed6fbeb18
("fatal-signal: Catch SIGSEGV and print backtrace"))

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

Compared to original packaging scheme within openvswitch, we removed
ovn-trace, ovn-detrace from openvswitch-ovn-common package.  ovn-detrace
requires python libs to run, so it does not actually work out of box in
previous builds anyway.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>