fix-resolve-home-v1

[RanVaknin]

For changes to files under the /model/ folder, and manual edits to autogenerated code (e.g. /service/s3/api.go) please create an Issue instead of a PR for those type of changes.

If there is an existing bug or feature this PR is answers please reference it here.
#4444

Added a fallback to resolve home using current user from "os/user".

[grrtrr]

This does not fix the problem with #4444, since os.UserHomeDir is also based on $HOME.
Test program to demonstrate:

// go build test.go
// env -i ./test
package main                                                                    
                                                                                
import (                                                                        
        "fmt"                                                                   
        "os"                                                                    
)                                                                               
                                                                                
func main() {                                                                   
        home, err := os.UserHomeDir()                                           
        fmt.Println(home,  err)                                            // prints "$HOME not defined" if variable is empty
}  

Better solution:

package main                                                                    
                                                                                
import (                                                                        
        "fmt"                                                                   
        "os/user"                                                               
)                                                                               
                                                                                
func main() {                                                                   
        user, err := user.Current()                                             
        fmt.Println(user.HomeDir, err)                  // Prints home directory even when running under env -i or $HOME unset.
}                                                                               

The user.Current() is based on getpwent and thus is independent of the $HOME variable.