Update system_info Collection to Include OSX and Build Version

[fligi7]

Issue: As it stands, the system_info collection does not collect or provide the OSX version (e.g., "10.12.4") nor the build version (e.g. "16E195").

Suggestion Solution:
Collect hostname and arch from uname, but collect the missing OSX version and Build version from the following plists (depending whether it's a workstation or server).

/System/Library/CoreServices/SystemVersion.plist
/System/Library/CoreServices/ServerVersion.plist

https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man1/sw_vers.1.html

$ plutil -p /System/Library/CoreServices/SystemVersion.plist
{
"ProductBuildVersion" => "16E195"
"ProductCopyright" => "1983-2017 Apple Inc."
"ProductVersion" => "10.12.4"
"ProductName" => "Mac OS X"
"ProductUserVisibleVersion" => "10.12.4"
}