Automatic merge from submit-queue

Add a custom main instead of the standard test main, to reduce stack …

Adds a custom test main handler (see: `TestMain` in https://golang.org/pkg/testing/ for details)

Partial fix for https://github.com/kubernetes/kubernetes/issues/25965

This does the standard timeout, but strips non-kubernetes stacks out of the stack trace (e.g. it filters things like:

```
goroutine 466 [IO wait, 7 minutes]:
net.runtime_pollWait(0x7fd74c4672c0, 0x72, 0xc821614000)
	/usr/local/go/src/runtime/netpoll.go:160 +0x60
net.(*pollDesc).Wait(0xc8215c21b0, 0x72, 0x0, 0x0)
	/usr/local/go/src/net/fd_poll_runtime.go:73 +0x3a
net.(*pollDesc).WaitRead(0xc8215c21b0, 0x0, 0x0)
	/usr/local/go/src/net/fd_poll_runtime.go:78 +0x36
net.(*netFD).Read(0xc8215c2150, 0xc821614000, 0x1000, 0x1000, 0x0, 0x7fd74c491050, 0xc820014058)
	/usr/local/go/src/net/fd_unix.go:250 +0x23a
net.(*conn).Read(0xc820a5a090, 0xc821614000, 0x1000, 0x1000, 0x0, 0x0, 0x0)
	/usr/local/go/src/net/net.go:172 +0xe4
net/http.noteEOFReader.Read(0x7fd74c465258, 0xc820a5a090, 0xc8215f0068, 0xc821614000, 0x1000, 0x1000, 0x405773, 0x0, 0x0)
	/usr/local/go/src/net/http/transport.go:1687 +0x67
net/http.(*noteEOFReader).Read(0xc8215ae1a0, 0xc821614000, 0x1000, 0x1000, 0xc82159ad1d, 0x0, 0x0)
	<autogenerated>:284 +0xd0
bufio.(*Reader).fill(0xc8202a2b40)
	/usr/local/go/src/bufio/bufio.go:97 +0x1e9
bufio.(*Reader).Peek(0xc8202a2b40, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0)
	/usr/local/go/src/bufio/bufio.go:132 +0xcc
net/http.(*persistConn).readLoop(0xc8215f0000)
	/usr/local/go/src/net/http/transport.go:1073 +0x177
created by net/http.(*Transport).dialConn
	/usr/local/go/src/net/http/transport.go:857 +0x10a6
```

We may want to get even more aggressive in the future.

@kubernetes/sig-testing