Read the proc status file when PID is given for metrics purpose.

To measure the MaxRSS memory correctly, read the proc status file
under /proc/<pid>/status and extract the MaxRSS value from it. The
implementation is only available for Linux based distributions.

Bug: b/169453825
Test: go test
Change-Id: I32e3068fee7447f9ef5dfb5a8d8dcb6934e0af23