catching Socketfs Inaccessible exceptions

[Steven Harp]

Experimenting with the VFS socket plugin, I'm tripping over
an exception that I'm not sure how to handle.  This is 
demonstrated in the "netty_tcp" test, which launches two
echo servers, one listening on port 80, and another on port
8080.  Both servers launch and become operational on about
25% of runs (under x86_64, nova kernel, QEMU, user network);
on the remaining starts, one of the servers succeeds, but the
other fails like this:

#+BEGIN_EXAMPLE
[init -> netty-server-8080] initialize server
[init -> netty-server-80] initialize server
[init -> netty-server-8080] sd=0
[init -> netty-server-8080] config: port=8080 read_write=0 nonblock=0
[init -> netty-server-8080] setsockopt: SO_REUSEADDR not yet implemented - always true
[init -> netty-server-80] sd=0
[init -> netty-server-80] config: port=80 read_write=0 nonblock=1
[init -> netty-server-80] setsockopt: SO_REUSEADDR not yet implemented - always true
[init -> netty-server-80] Error: plugin()->open("/socket/tcp/2/listen") failed
[init -> netty-server-80] Error: _fd_for_type: listen file not accessible
[init -> netty-server-8080] test in blocking mode
[init -> netty-server-80] Error: Uncaught exception of type 'Socket_fs::Context::Inaccessible'
[init -> netty-server-80] Warning: abort called - thread: ep
[init] child "netty-server-80" exited with exit value 1
#+END_EXAMPLE

Empirically, it appears that the server that gets past "setsockopt:..."
first will become operational--the other server usually will not.
The order seems to be non-deterministic. 

Its not clear how to catch the 'Socket_fs::Context::Inaccessible' exception
in the netty server code, or even if that is an appropriate response.

Suggestions?

 - Steve Harp