discoverd, router: Use SO_REUSEPORT.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
all: Update Godeps to include go_reuseport.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
controller, bootstrap: Pass through the HostNetwork option.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
router: The router listeners themselves should be reusable too.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
Merge pull request #541 from flynn/so-reuseport

SO_REUSEPORT