Always show RemoteSocket.Exists in json

The `Exists` field of the `RemoteSocket` struct is marshaled to json with the
`omitempty` setting. This has the disadvantage that by default `podman info`
shows a `remotePath` entry (the remote path is set in
`pkg/domain/infra/abi/systems.go`: `(*ContainerEngine).Info`) but not that this
path does not exist:
```
❯ podman info --format json | jq .host.remoteSocket
{
  "path": "/run/user/1000/podman/podman.sock"
}
```

By removing the `omitempty`, we ensure that the existence is always shown:
```
❯ bin/podman info --format json | jq .host.remoteSocket
{
  "path": "/run/user/1000/podman/podman.sock",
  "exists": false
}
```

Signed-off-by: Dan Čermák <dcermak@suse.com>

libpod/define/info.go

@@ -68,7 +68,7 @@ type HostInfo struct {
 // RemoteSocket describes information about the API socket
 type RemoteSocket struct {
 	Path   string `json:"path,omitempty"`
-	Exists bool   `json:"exists,omitempty"`
+	Exists bool   `json:"exists"`
 }
 
 // SlirpInfo describes the slirp executable that is being used

test/e2e/info_test.go

@@ -118,6 +118,8 @@ var _ = Describe("Podman Info", func() {
 		Expect(session).Should(Exit(0))
 		if IsRemote() {
 			Expect(session.OutputToString()).To(ContainSubstring("true"))
+		} else {
+			Expect(session.OutputToString()).To(ContainSubstring("false"))
 		}
 
 	})