fix(deisctl): properly resolve ~ in path

While `$HOME` is resolved properly in paths, `~` is not
and requires special handling.

I tested this with the following, on both bash and zsh:
```console
$ deisctl config platform set sshPrivateKey=$HOME/.ssh/deis
$ deisctl config platform set sshPrivateKey=~/.ssh/deis
$ deisctl config platform set sshPrivateKey=/Users/carmstrong/.ssh/deis
$ DEISCTL_UNITS=/Users/carmstrong/gocode/src/github.com/deis/deis/deisctl/units deisctl refresh-units
$ DEISCTL_UNITS=$HOME/gocode/src/github.com/deis/deis/deisctl/units deisctl refresh-units
$ DEISCTL_UNITS=~/gocode/src/github.com/deis/deis/deisctl/units deisctl refresh-units
```

fixes #2677

Author: carmstrong

deisctl/cmd/cmd.go

@@ -6,7 +6,6 @@ import (
 	"io/ioutil"
 	"net/http"
 	"os"
-	"path"
 	"path/filepath"
 	"regexp"
 	"strconv"
@@ -631,9 +630,7 @@ Options:
 		os.Exit(2)
 	}
 	dir := args["--path"].(string)
-	if dir == "$HOME/.deis/units" || dir == "~/.deis/units" {
-		dir = path.Join(os.Getenv("HOME"), ".deis", "units")
-	}
+	dir = utils.ResolvePath(dir)
 	// create the target dir if necessary
 	if err := os.MkdirAll(dir, 0755); err != nil {
 		return err

deisctl/config/config.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"strings"
+
+	"github.com/deis/deis/deisctl/utils"
 )
 
 // Config runs the config subcommand
@@ -72,7 +74,7 @@ func doConfigSet(client *etcdClient, root string, kvs []string) ([]string, error
 
 		// special handling for sshKey
 		if path == "/deis/platform/sshPrivateKey" {
-			b64, err := readSSHPrivateKey(v)
+			b64, err := readSSHPrivateKey(utils.ResolvePath(v))
 			if err != nil {
 				return result, err
 			}

deisctl/utils/utils.go

@@ -2,7 +2,11 @@
 
 package utils
 
-import "fmt"
+import (
+	"fmt"
+	"os"
+	"strings"
+)
 
 // DeisIfy returns a pretty-printed deis logo along with the corresponding message
 func DeisIfy(message string) string {
@@ -17,3 +21,11 @@ func DeisIfy(message string) string {
 		square, circle, triangle, title,
 		triangle, square, circle, reset)
 }
+
+// ResolvePath returns the path with a tilde (~) and $HOME replaced by the actual home directory
+func ResolvePath(path string) string {
+	path = strings.Replace(path, "~", os.Getenv("HOME"), -1)
+	// Using $HOME seems to work just fine with `deisctl config`, but not `deisctl refresh-units`
+	path = strings.Replace(path, "$HOME", os.Getenv("HOME"), -1)
+	return path
+}