If -test.timeout is not specified to go test, it will time out after
a default 10 minutes.

The iOS exec wrapper also contains a fail safe timeout mechanism for
a stuck device. However, if no explicit -test.timeout is specified,
it will use a timeout of 0, plus some constant amount.

Use the same default timeout in the exec wrapper as for go test,
10 minutes.

Change-Id: I6465ccd9f7b9ce08fa302e6697f7938a0ea9af34
Reviewed-on: https://go-review.googlesource.com/36062Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>