tools: hv: Return the full kernel version

Currently, we are returning the same string for both OSBuildNumber
and OSVersion keys. Return the full uts string for the OSBuild
key since Windows does not impose any restrictions on this.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Reported-by: Claudio Latini <claudio.latini@live.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>