Consistently use bytes for memory statistics

For some reason, stat_collector assumed rss was reported in kilobytes
instead of bytes and multiplied it by 1024.  The rest of the code then
started to divide the 'used_memory_in_bytes' by 1024 to really get bytes
back.  Very odd.

This change simply removes the hacks that multiply and divide to get
expected data.
Make memory reported match cgroup usage data

The DEA was reporting 'used_memory_in_bytes' as the RSS returned from
warden.  RSS, however, is not what cgroup uses when checking container
memory limits so it's inappropriate memory statistic to report to end
users via cf stats.

The Linux cgroup implementation reports container memory usage in
memory/memory.usage_in_bytes and calculates this by adding
memory/memory.stat:cache and memory/memory.stat:rss so this change will
introduce the same logic to the DEA.  Instead of using cache and rss,
however, total_rss and total_cache will be used as it accounts for child
containers when present.
Merge branch 'used-is-rss-plus-cache' of https://github.com/sykesm/dea_ng into sykesm-used-is-rss-plus-cache

Signed-off-by: Michael Maximilien <maxim@us.ibm.com>

Conflicts:
	lib/dea/starting/instance.rb
	lib/dea/stat_collector.rb
	spec/unit/starting/instance_spec.rb
	spec/unit/stat_collector_spec.rb