support get_package_version for smartos

Hi,

I write `#get_package_version` for joyent smartos.

## Case success

```
> backend.check_os
=> {:family=>"SmartOS", :release=>nil}

> backend.get_package_version('openssl')
=> #<SpecInfra::CommandResult:0x007fb82e1b8be8
 @exit_signal=nil,
 @exit_status=0,
 @stderr="",
 @stdout="openssl-1.0.1fnb1\n">
```

## Case fail

```
> backend.get_package_version('openss')
=> #<SpecInfra::CommandResult:0x007fb82e309588
 @exit_signal=nil,
 @exit_status=1,
 @stderr="",
 @stdout="">
```