Cache only a small portion of page map data.

The scudo memory allocator will allocate a large virtual memory address
that causes procrank to allocate a huge amount of data. Modify so it
caches the data a bit at a time.

Remove some allocations that are not necessary since the data is only used
in the first loop.

Fix a few pread64 checks against the actual bytes read, rather than the
read is < 0.

Fix sort by rss in procrank.

Bug: 135694447

Test: Ran unit tests (only one unit test actually runs the modified code).
Test: Ran the old version of procrank using a static libmeminfo and verified
Test: that the same data is found as the new version.

Change-Id: I8adc169b5607ec994ff13a9e161a479350d84c4d