Make resident memory size expectation less precise
Make resident memory size expectation less precise

- The virtual memory size varies by operating system, so the most accurate
promise we can make is that is should be greater-than-or-equal to the
resident memory size.

[#152736258](https://www.pivotaltracker.com/story/show/152736258)

Signed-off-by: Kai Hofstetter <d8bd5286cafb8056b3612939db697751b39d6de8@sap.com>

cloudfoundry/gosigar,cloudfoundry/gosigar