proxy/vm: Set ctl/io sockets to nil after goroutine have finished
proxy/vm: Set ctl/io sockets to nil after goroutine have finished

Tests were sometimes panicking with null derefences (found by the unit
tests!) when trying to access those socket objects.

Indeed, we have to wait for the goroutine those objects to be finished
instead of just after closing the sockets.

Signed-off-by: Damien Lespiau <64bd3cb94f359c1a3ce68dae5e26b40578526277@intel.com>

clearcontainers/proxy,dlespiau/proxy,dlespiau/clearcontainers-proxy,clearcontainers/proxy,dlespiau/clearcontainers-proxy,dlespiau/proxy