bionic: change properties benchmarks to read a single property

The properties benchmarks were reading n properties from a property
area with n properties in it, which was making it hard to compare
the time between runs of different sizes.  Change the benchmark
to read a random property per iteration so the numbers between
runs are comparable.

Change-Id: Ib1648ce0948d9038fce76d209608427376cfb8da
1 file changed