cmd/vendor/github.com/google/pprof/internal/driver: skip read only dir error on Android

On an android/amd64 emulator, $HOME points to / which is not writable.
Ignore the error in the pprof driver test.

With this, androidtest.sh on android/amd64 and android/386 passes.

Upstream pull request https://github.com/google/pprof/pull/295.

Change-Id: If919d7f44530a977fd044631ad01bac87d32deaa
Reviewed-on: https://go-review.googlesource.com/88817


Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>