[buildbot] phase1: switch away from deprecated slave side Git step

[LEDE Commits]

jow pushed a commit to buildbot.git, branch master:
https://git.lede-project.org/8baf1e26f76576aa933bb18e486590e3dac35811

commit 8baf1e26f76576aa933bb18e486590e3dac35811
Author: Jo-Philipp Wich <jo at mein.io>
AuthorDate: Mon Nov 28 19:31:46 2016 +0100

    phase1: switch away from deprecated slave side Git step
    
    Signed-off-by: Jo-Philipp Wich <jo at mein.io>
---
 phase1/master.cfg | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/phase1/master.cfg b/phase1/master.cfg
index 2ae92f1..bbed054 100644
--- a/phase1/master.cfg
+++ b/phase1/master.cfg
@@ -147,7 +147,7 @@ c['schedulers'].append(ForceScheduler(
 # only take place on one slave.
 
 from buildbot.process.factory import BuildFactory
-from buildbot.steps.source import Git
+from buildbot.steps.source.git import Git
 from buildbot.steps.shell import ShellCommand
 from buildbot.steps.shell import SetProperty
 from buildbot.steps.transfer import FileUpload
@@ -274,7 +274,11 @@ for target in targets:
 		))
 
 	# check out the source
-	factory.addStep(Git(repourl=repo_url, branch=repo_branch, mode='update'))
+	factory.addStep(Git(
+		repourl = repo_url,
+		branch = repo_branch,
+		mode = 'incremental',
+		method = 'clean'))
 
 	factory.addStep(ShellCommand(
 		name = "rmtmp",