tests: Widely switch to new commit/branch syntax

Lift most test cases to the new syntax, just with few exceptions:
 - tests/test_refspec/test2.yml actually stresses the mixed usage
   (but clean per repo)
 - tests/test_repo_includes references kas as external repo at a point
   where there was no new syntax yet; this needs to be migrated
   differently later on

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

tests/test_refspec/test.yml

@@ -1,13 +1,13 @@
 header:
-  version: 8
+  version: 14
 
 repos:
   this:
 
   kas:
     url: https://github.com/siemens/kas.git
-    refspec: 907816a5c4094b59a36aec12226e71c461c05b77
+    commit: 907816a5c4094b59a36aec12226e71c461c05b77
 
   kas2:
     url: https://github.com/siemens/kas.git
-    refspec: master
+    branch: master

tests/test_refspec/test2.yml

@@ -1,13 +1,14 @@
 header:
-  version: 8
+  version: 14
 
 repos:
   this:
 
   kas:
     url: https://github.com/siemens/kas.git
-    refspec: master
+    branch: master
 
   kas2:
     url: https://github.com/siemens/kas.git
+    # keep legacy refspec here for testing purposes
     refspec: 907816a5c4094b59a36aec12226e71c461c05b77

tests/test_refspec/test3.yml

@@ -1,13 +1,13 @@
 header:
-  version: 8
+  version: 14
 
 repos:
   this:
 
   kas_abs:
     url: https://github.com/siemens/kas.git
-    refspec: refs/heads/master
+    branch: refs/heads/master
 
   kas_rel:
     url: https://github.com/siemens/kas.git
-    refspec: master
+    branch: master