return errors instead of logrus.Fatal calls

This commit refactors the code to remove more or less
all occurences of logrus.Fatalf() from the code under
pkg/ except for app.go where all the errors are being
handled currently.

This is being done since random logrus.Fatalf() calls
all around the code was making handling the errors,
unit testing and troubleshooting a bit more painful.

logrus.Fatalf() calls are either replaced by
return errors.New("new error")
or
return errors.Wrap(err, "annonate error")
calls, and the function signatures are accordingly
changed to accomodate the new return values.

The unit tests which previously used to check
if logrus.Fatalf() calls worked fine have also
been fixed to only check for errors now.

Fixes #416

pkg/app/app.go

@@ -35,6 +35,7 @@ import (
 
 	"os"
 
+	"github.com/fsouza/go-dockerclient/external/github.com/Sirupsen/logrus"
 	"github.com/kubernetes-incubator/kompose/pkg/kobject"
 	"github.com/kubernetes-incubator/kompose/pkg/loader"
 	"github.com/kubernetes-incubator/kompose/pkg/transformer"
@@ -211,16 +212,26 @@ func Convert(opt kobject.ConvertOptions) {
 	komposeObject := kobject.KomposeObject{
 		ServiceConfigs: make(map[string]kobject.ServiceConfig),
 	}
-	komposeObject = l.LoadFile(opt.InputFiles)
+	komposeObject, err = l.LoadFile(opt.InputFiles)
+	if err != nil {
+		logrus.Fatalf(err.Error())
+	}
 
 	// Get a transformer that maps komposeObject to provider's primitives
 	t := getTransformer(opt)
 
 	// Do the transformation
-	objects := t.Transform(komposeObject, opt)
+	objects, err := t.Transform(komposeObject, opt)
+
+	if err != nil {
+		logrus.Fatalf(err.Error())
+	}
 
 	// Print output
-	kubernetes.PrintList(objects, opt)
+	err = kubernetes.PrintList(objects, opt)
+	if err != nil {
+		logrus.Fatalf(err.Error())
+	}
 }
 
 // Up brings up deployment, svc.
@@ -237,7 +248,10 @@ func Up(opt kobject.ConvertOptions) {
 	komposeObject := kobject.KomposeObject{
 		ServiceConfigs: make(map[string]kobject.ServiceConfig),
 	}
-	komposeObject = l.LoadFile(opt.InputFiles)
+	komposeObject, err = l.LoadFile(opt.InputFiles)
+	if err != nil {
+		logrus.Fatalf(err.Error())
+	}
 
 	// Get the transformer
 	t := getTransformer(opt)
@@ -263,7 +277,10 @@ func Down(opt kobject.ConvertOptions) {
 	komposeObject := kobject.KomposeObject{
 		ServiceConfigs: make(map[string]kobject.ServiceConfig),
 	}
-	komposeObject = l.LoadFile(opt.InputFiles)
+	komposeObject, err = l.LoadFile(opt.InputFiles)
+	if err != nil {
+		logrus.Fatalf(err.Error())
+	}
 
 	// Get the transformer
 	t := getTransformer(opt)