Test that relro sharing actually saves memory.

Test that relro sharing actually saves memory.

Spawn 20 child processes, have them all load the library, and compare
the total PSS used in the case where we use dlopen() and the case where
we use android_dlopen_ext() with relro sharing. We assume we will save
at least 10% of the memory; in practise this example saves 40% or more
so this should be a reasonable threshold.

Bug: 14299541
Change-Id: Idccf6b8b0eb137abae2200f1ce68fb76b3cbdd75