Vendor packages and add Makefile

* Vendors packages
  * Adds a Makefile that uses docker to build a static binary against musl
using alpine linux.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

vendor/github.com/pkg/sftp/debug.go

@@ -0,0 +1,9 @@
+// +build debug
+
+package sftp
+
+import "log"
+
+func debug(fmt string, args ...interface{}) {
+	log.Printf(fmt, args...)
+}