Squish: Refactor selecting configured Kits in project

The design of the Projects mode changed several times. We wrote lots of
workarounds to keep even more old code alive because we never had the time
for a proper refactoring. This time is now.

Leads to more stable code with far less variables flying around.

Task-number: QTCREATORBUG-20265
Change-Id: I29e5956ea3279cdb1d6da61bf5b461666de436bc
Reviewed-by: Robert Loehning <robert.loehning@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

tests/system/shared/classes.py

@@ -81,6 +81,13 @@ class Targets:
             test.fatal("You've passed at least one unknown target!")
         return result
 
+    @staticmethod
+    def getIdForTargetName(targetName):
+        for id in Targets.ALL_TARGETS:
+            if Targets.getStringForTarget(id) == targetName:
+                return id
+        raise Exception("'%s' is not a known target name" % targetName)
+
     @staticmethod
     def getDefaultKit():
         return Targets.DESKTOP_5_6_1_DEFAULT