Adds raw disk utils

Adds raw disk utils to convert a raw disk into a GCE or Azure image
Adds a new constants package to store constants that can be reused
across all of our projects
Expands KairosFs interface to be in line with whats used on other
projects so we can use it

constants/constants.go

@@ -0,0 +1,8 @@
+// Package constants This file contains all the constants that can be reused across the project
+package constants
+
+const (
+	MB       = int64(1024 * 1024)
+	GB       = 1024 * MB
+	FilePerm = 0644
+)