system: add {set/get}_computer_name
system: add {set/get}_computer_name

Add {set/get}_computer_name for setting/getting
computer hostname. I add this in system module to be
the same as on windows, creating a cross-platform
way to interact with computer's hostname.

Signed-off-by: Heghedus Razvan <0a60b1373e874cee2eab52b3c98f4647a58e91af@ni.com>

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt