implements patch support for repos

With this commit its now possible to patch 3rd party repos before bitbake is started.

Example:

This is our repo:
  .
  ├── kas.yml
  ├── first-patch.patch
  └── quilt-patches
      ├── second-patch.patch
      ├── third-patch.patch
      └── series

Content of kas.yml:
  header:
    version: 8

  repos:
    my:
    third-party:
      url: "git://example.com/third-party.git"
      refspec: "35adf4...34"
      patches:
        01-first:
          repo: my
          path: "first-patch.patch"
        02-second:
          repo: my
          path: "quilt-patches"

Currently only 'git' repositories can be patched.

Signed-off-by: Claudius Heine <ch@denx.de>

kas/shell.py

@@ -30,7 +30,7 @@ from kas.libkas import kasplugin
 from kas.config import Config
 from kas.libcmds import (Macro, Command, SetupDir, SetupProxy, SetupEnviron,
                          WriteConfig, SetupHome, ReposFetch, ReposCheckout,
-                         CleanupSSHAgent, SetupSSHAgent)
+                         ReposApplyPatches, CleanupSSHAgent, SetupSSHAgent)
 
 __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017'
@@ -91,13 +91,15 @@ class Shell:
         if not args.keep_config_unchanged:
             macro.add(ReposFetch())
             macro.add(ReposCheckout())
-            macro.add(SetupEnviron())
+
+        macro.add(SetupEnviron())
+        macro.add(SetupHome())
+
+        if not args.keep_config_unchanged:
+            macro.add(ReposApplyPatches())
             macro.add(WriteConfig())
-        else:
-            macro.add(SetupEnviron())
 
         # Shell
-        macro.add(SetupHome())
         macro.add(ShellCommand(args.command))
 
         if 'SSH_PRIVATE_KEY' in os.environ: