nacl skips this test, and so do we now

This test tests some various linker output, which we don't quite handle
correctly, apparently.  Netierh does nacl, though, so we punt for now.
No need to cleanup on the server side after test.
Store the output of the rpc in a file, not a var

Previously I was storing this output in a bash variable and parsing
things from there. The problem, however, is that certaion go tests
purposefully print the '\0' character to stdout, which bash variables
silently ignore and strip from their output when echoed. This causes us
to fail at least one go test.  Creating an actual file in the file
system and always catting from there avoids this issue.
Initialize overflow of hash buckets to nil before use.

Without doing this we were getting strange segfaults for addresses down
in the 0xff00 range when dereferencing the b->overflow field in
hash_insert().

I narrowed down the problem to only occurring after reentering the
"again" loop as the result of hash_grow() invalidating the entire
hashmap.  When hash_grow() returns, h->buckets points to a completely
new region for holding buckets, but a reference to the original set of
buckets is kept in h->oldbuckets, so that entries from it can be
lazily copied out on demand. The memory for the new h->buckets seems
to have been reaped from the garbage collector (not a new mmap).

In the case when we enter the "again" loop after a hash_grow(), we end
up calling grow_work(), which calls evacuate(), which has some crazy
logic for figuring out which parts of our original bucket to copy out
from h->oldbuckets[i] to the new h->buckets[i]. This logic doesn't
seem to 0 out the overflow field of the new buckets by default.  If
the reaped memory wasn't zeroed out before handing it back to us, we
get screwed.  I'm not sure what the normal semantics for this are with
the go garbage collector.

Anyway, simply adding a few lines to the evacuate() function before
any other copying is done:

        x->overflow = nil;
        y->overflow = nil;

seems to fix the problem, and all other go tests still function as
expected -- both on linux and on akaros. Given that they don't even have
this file in the tip of their hg repo anymore, I'm committing this small
change here and moving on.