[kernel/net] commandserver: replace boost::asio with libevent library

The other part of kernel/net didn't compile, because of the difference
between boost:;asio and libevent.

After all patches in this set, we need to rebase it to one.
[kernel/net] session: replace boost::asio with libevent library

This patch only allow to compile session module, it can not work
correct however.

Need in rebasing.
[kernel/net] commandserver: add assert after evconnlistener_new_bind()
[kernel/net] don't truncate socket path
[kernel/net] commandserver: add event_base_loop()
[kernel/net] session: pass session instance to asyncRead() cb for bufev
[kernel/net] dro ioservicepool (deprecated workers for boost::asio)
[kernel/net] avoid leaking session and it's buffer event
[kernel/net] session: drop asio headers
[kernel/net] commandserver: move asio headers into module (was in header)
[kernel/net] commandserver: todo about signal handlers