Include only subset of memory statistics in diagnostic data

Current design collects all memory-related statistics from /proc/meminfo. This is quite a large number of metrics, which increases the amount of data collected, and a large portion are exotic kernel-internal statistics unlikely to be useful. We should include only the following initially:

MemTotal
Cached
Dirty
Buffers
MemFree
SwapTotal
SwapCached
SwapFree
Active
Inactive
Active(anon)
Inactive(anon)
Active(file)
Inactive(file)