all: test adjustments for the iOS builder

The working directory is now adjusted to match the typical Go test
working directory in main, as the old trick for adjusting earlier
stopped working with the latest version of LLDB bugs.

That means the small number of places where testdata files are
read before main is called no longer work. This CL adjusts those
reads to happen after main is called. (This has the bonus effect of
not reading some benchmark testdata files in all.bash.)

Fixes compress/bzip2, go/doc, go/parser, os, and time package
tests on the iOS builder.

Change-Id: If60f026aa7848b37511c36ac5e3985469ec25209
Reviewed-on: https://go-review.googlesource.com/35255


Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>