The iOS test harness dumps the output of its lldb session to stdout,
but only if the lldb session was successfully started.
Make sure the log is always dumpede, so that lldb startup failures
such as

lldb setup error: exited (lldb start: exit status 253)

can be diagnosed.

For the iOS builders.

Change-Id: Ie0e3341dd8f84a88d26509c34816668d3ebbfaa0
Reviewed-on: https://go-review.googlesource.com/76195
Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>