prompt-less signing via passphrase file

To support signing images without prompting the user, add CLI flags for
providing a passphrase file.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

vendor/github.com/proglottis/gpgme/callbacks.go

@@ -0,0 +1,42 @@
+package gpgme
+
+import (
+	"sync"
+)
+
+var callbacks struct {
+	sync.Mutex
+	m map[uintptr]interface{}
+	c uintptr
+}
+
+func callbackAdd(v interface{}) uintptr {
+	callbacks.Lock()
+	defer callbacks.Unlock()
+	if callbacks.m == nil {
+		callbacks.m = make(map[uintptr]interface{})
+	}
+	callbacks.c++
+	ret := callbacks.c
+	callbacks.m[ret] = v
+	return ret
+}
+
+func callbackLookup(c uintptr) interface{} {
+	callbacks.Lock()
+	defer callbacks.Unlock()
+	ret := callbacks.m[c]
+	if ret == nil {
+		panic("callback pointer not found")
+	}
+	return ret
+}
+
+func callbackDelete(c uintptr) {
+	callbacks.Lock()
+	defer callbacks.Unlock()
+	if callbacks.m[c] == nil {
+		panic("callback pointer not found")
+	}
+	delete(callbacks.m, c)
+}