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/build.py

@@ -29,7 +29,7 @@ from .libkas import find_program, run_cmd, kasplugin
 from .libcmds import (Macro, Command, SetupDir, SetupProxy,
                       CleanupSSHAgent, SetupSSHAgent, SetupEnviron,
                       WriteConfig, SetupHome, ReposFetch,
-                      ReposCheckout)
+                      ReposApplyPatches, ReposCheckout)
 
 __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017'
@@ -86,11 +86,12 @@ class Build:
         macro.add(ReposFetch())
         macro.add(ReposCheckout())
         macro.add(SetupEnviron())
+        macro.add(SetupHome())
+        macro.add(ReposApplyPatches())
 
         macro.add(WriteConfig())
 
         # Build
-        macro.add(SetupHome())
         macro.add(BuildCommand(args.task))
 
         if 'SSH_PRIVATE_KEY' in os.environ: