Fix misc stuff found by jhonce

During the python client implementation, jhonce found some return types
that needed correction as well as a panic related to history which is now
corrected.

Signed-off-by: baude <bbaude@redhat.com>

Closes: #704
Approved by: rhatdan

cmd/podman/varlink/io.projectatomic.podman.varlink

@@ -88,11 +88,11 @@ method InspectImage(name: string) -> (image: string)
 method HistoryImage(name: string) -> (history: []ImageHistory)
 method PushImage(name: string, tag: string, tlsverify: bool) -> ()
 method TagImage(name: string, tagged: string) -> ()
-method RemoveImage(name: string, force: bool) -> ()
+method RemoveImage(name: string, force: bool) -> (image: string)
 method SearchImage(name: string, limit: int) -> (images: []ImageSearch)
 method DeleteUnusedImages() -> (images: []string)
 method CreateFromContainer() -> (notimplemented: NotImplemented)
-method ImportImage(source: string, reference: string, message: string, changes: []string) -> (id: string)
+method ImportImage(source: string, reference: string, message: string, changes: []string) -> (image: string)
 method ExportImage(name: string, destination: string, compress: bool) -> ()
 method PullImage(name: string) -> (id: string)