config: Update shared config loading to use os.UserHomeDir() (#1563)

Instead of hard-coding Windows and *nix environment variables, rely on
os.UserHomeDir() to do the right thing. Ignore errors since those only
happen in situations we don't care about (and didn't handle
previously).

Signed-off-by: Stephen Kitt <skitt@redhat.com>
Co-authored-by: Jason Del Ponte <961963+jasdel@users.noreply.github.com>

.changelog/4f325261c632499cb3f4464799763f58.json

@@ -0,0 +1,8 @@
+{
+    "id": "4f325261-c632-499c-b3f4-464799763f58",
+    "type": "bugfix",
+    "description": "Updates `config` module to use os.UserHomeDir instead of hard coded environment variable for OS. [#1563](https://github.com/aws/aws-sdk-go-v2/pull/1563)",
+    "modules": [
+        "config"
+    ]
+}

config/shared_config.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strings"
 	"time"
 
@@ -1051,12 +1050,9 @@ func (e CredentialRequiresARNError) Error() string {
 }
 
 func userHomeDir() string {
-	if runtime.GOOS == "windows" { // Windows
-		return os.Getenv("USERPROFILE")
-	}
-
-	// *nix
-	return os.Getenv("HOME")
+	// Ignore errors since we only care about Windows and *nix.
+	homedir, _ := os.UserHomeDir()
+	return homedir
 }
 
 func oneOrNone(bs ...bool) bool {