Connection broken in test cases

#### Version information:

> go-ipfs version: 0.4.11-dev-38a9be5a0
Repo version: 5
System version: amd64/linux
Golang version: go1.8.3

#### Type:

Bug

#### Severity:

Very Low

#### Description:

I got the following errors when running one of the sharness tests (appears to be unrelated to the precise test). Note: the daemon didn't die, the connection just appears to have terminated prematurely.

```
HTTP/1.x transport connection broken
```

Full output (from `test/sharness/t0040-add-and-cat.sh`):
```
expecting success:
mkdir -p named-pipe-dir &&
mkfifo named-pipe-dir/named-pipe &&
test_expect_code 1 ipfs add -r named-pipe-dir 2>actual &&
printf "Error:$err_prefix Unrecognized file type for named-pipe-dir/named-pipe: $(generic_stat named-pipe-dir/named-pipe)\n" >expected &&
rm named-pipe-dir/named-pipe &&
rmdir named-pipe-dir &&
test_cmp expected actual

> diff -u expected actual
--- expected 2017-07-31 22:25:41.398822000 +0000
+++ actual 2017-07-31 22:25:41.398822000 +0000
@@ -1 +1 @@
-Error: Post http://127.0.0.1:46644/api/v0/add?encoding=json&progress=true&r=true&stream-channels=true: Unrecognized file type for named-pipe-dir/named-pipe: prw-rw-r--
+Error: Post http://127.0.0.1:46644/api/v0/add?encoding=json&progress=true&r=true&stream-channels=true: net/http: HTTP/1.x transport connection broken: Unrecognized file type for named-pipe-dir/named-pipe: prw-rw-r--
not ok 190 - useful error message when recursively adding a named pipe
```