[net]linux: start replacing lsof

Provide correct length for slice creation.

- Creating a slice of length numFDs and later appending elements to it
  results in a slice whose first numFDs elements are all nil. It is
  sufficient to create a slice of zero length since we are appending
  elements to it.
- The current allocation will make ret a slice of length 0. What's
  needed is a slice of length len(ofs).

NewProcess does not close file descriptor

process: add CmdlineSlice function for linux + freebsd

darwin will not perform correctly if there are spaces in the actual
arguments, in which case a single argument will be reported as
multple. Some CGO would be needed to get around this I think.

I couldn't find any good documentation on how windows handles
command line arguments with spaces inside the actual arguments, so
this implementation merely just splits on spaces.

process: change linux NewProcess to only stat /proc/[pid]

Before it was doing a fillFromStatus() call which was much slower
and none of the information was needed, except by the Name() func
which now will call fillFromStatus() if p.name is not set.

Sometimes (at least on linux) cmdline is empty, this was causing
a panic.

This allows for getting more exact information about each argument
especially if there are arguments that have spaces in them.

This was not implemented for darwin or for windows because they
both currently have not way of properly parsing the cmdline string.
Darwin parses the output of 'ps' which is already whitespace
segmented, and windows just has the cmdline string.

[load]all: add Misc in load to get miscellaneous host info from /proc…

Add test for process.CPUTimes()

Document + add tests for for mem.VirtualMemory()

This change changes and documents the (previously undocumented) behavior of Used
to "RAM used by programs".

We also remove the undocumented and unused Shared field of that struct.

So with this change in place, the VirtualMemoryStruct contains:
* three human-consumable fields for Total, Used and Available memory
* one human-consumable UsedPercentage field
* a number of kernel specific fields

Use OS calls rather than exec() to get memory stats on Darwin