runtime/pprof: disable new memory test

It cannot run 'go tool pprof'. There is no guarantee that's installed.
It needs to build a temporary pprof binary and run that.
It also needs to skip the test on systems that can't build and
run binaries, namely android and nacl.

See src/cmd/nm/nm_test.go's TestNM for a template.

Update issue 8867
Status: Accepted

TBR=dvyukov
CC=golang-codereviews
https://codereview.appspot.com/153710043