expose tcp_read/ssl_read errors

[jiahuang]

This PR exposes HCI 1008 (select) errors on read so that it can be handled in the JS layer.

[natevw]

This is wrong. tm_tcp_read returns errno on error:
https://github.com/tessel/runtime/blob/master/src/posix/tm_net.c#L169

…which at least for the POSIX-defined errors are mandated to have positive values: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/errno.h.html

So: any non-zero value indicates error…the sign of the number should not be checked here, or you will certainly miss errors under POSIX (and probably CC3K too unless it happens to provide negative errno values of its own…).

[natevw]

Glad this is getting hooked up — please see comments on patch though for some logic changes necessary to make it work as you intend for the tcp case especially.

[tcr]

This is the opposite of staying silent

[tcr]

But yeah, should we have internal code be emitting console.logs if it's just going to throw the error immediately?

[natevw]

@jiahuang is this just tying up loose ends, or was the missing error handling related to tessel/t1-firmware#128 too?