fix(dbusservice): Use array of strings maps arguments types for GetAu…

…thenticationModes (#227)

The method accepts a slice of maps and returns another slice of maps, so
we should respect that in the introspection data

UDENG-5321

Related to ubuntu/authd#628

internal/dbusservice/dbusservice.go

@@ -15,16 +15,16 @@ const intro = `
 <node>
 	<interface name="%s">
 		<method name="NewSession">
-		<arg type="s" direction="in" name="username"/>
-		<arg type="s" direction="in" name="lang"/>
-		<arg type="s" direction="in" name="mode"/>
-		<arg type="s" direction="out" name="sessionID"/>
-		<arg type="s" direction="out" name="encryptionKey"/>
+			<arg type="s" direction="in" name="username"/>
+			<arg type="s" direction="in" name="lang"/>
+			<arg type="s" direction="in" name="mode"/>
+			<arg type="s" direction="out" name="sessionID"/>
+			<arg type="s" direction="out" name="encryptionKey"/>
 		</method>
 		<method name="GetAuthenticationModes">
-		<arg type="s" direction="in" name="sessionID"/>
-		<arg type="a{ss}" direction="in" name="supportedUILayouts"/>
-		<arg type="a{ss}" direction="out" name="authenticationModes"/>
+			<arg type="s" direction="in" name="sessionID"/>
+			<arg type="aa{ss}" direction="in" name="supportedUILayouts"/>
+			<arg type="aa{ss}" direction="out" name="authenticationModes"/>
 		</method>
 		<method name="SelectAuthenticationMode">
 			<arg type="s" direction="in" name="sessionID"/>