Migrate aslr test to gtest.

Migrate aslr test to gtest.

Create tests which test the values of mmap_rnd_bits, and
mmap_rnd_compat_bits, if applicable, and verify that the address space
is randomized as expected given the provided values.

Also add a pair of tests to CTS that enforce that the observed entropy
is at least as high as a designated value.  That value will start as our
default value, which also corresponds to the maximum value of some
configurations.

Packaging of executables along with a nativetest suite is not supported,
so add a dummy nativetest suite, scrape_mmap_addr, which ensure that the
executables are present along with the given tests at predictable
locations.

Bug: 26512380
Change-Id: Ib1202984f9b98c503b8d3bc2c2248a9d06940845