enable dnsplugin for network create

when users create a new network and the dnsname plugin can be found by
podman, we will enable container name resolution on the new network.
there is an option to opt *out* as well.

tests cannot be added until we solve the packaging portion of the
dnsname plugin.

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

pkg/network/netconflist.go

@@ -2,6 +2,8 @@ package network
 
 import (
 	"net"
+	"os"
+	"path/filepath"
 )
 
 // NcList describes a generic map
@@ -111,3 +113,22 @@ func NewFirewallPlugin() FirewallConfig {
 		Backend:    "iptables",
 	}
 }
+
+// NewDNSNamePlugin creates the dnsname config with a given
+// domainname
+func NewDNSNamePlugin(domainName string) DNSNameConfig {
+	return DNSNameConfig{
+		PluginType: "dnsname",
+		DomainName: domainName,
+	}
+}
+
+// HasDNSNamePlugin looks to see if the dnsname cni plugin is present
+func HasDNSNamePlugin(paths []string) bool {
+	for _, p := range paths {
+		if _, err := os.Stat(filepath.Join(p, "dnsname")); err == nil {
+			return true
+		}
+	}
+	return false
+}