add OS uptime information to os::print_os_info output

Currently os::print_os_info outputs various interesting OS Information.
The output is platforms dependent, on Linux currently the following information is printed :
distro, uname, some important libversions, some limits, load average, memory info, info about /proc/sys, container and virtualization details and steal ticks.
The OS uptime would be a helpful addition.

This change adds a line of output giving the uptime in days, hours and minutes:
  "OS uptime <num> days <num>:<num> hours"

This Information can be found in a hs_err file.
Often, a recent reboot indicates that the undelying System has been changed (OS update etc). This might be the cause of the crash that produced the hs_err file.