[buildbot] phase1: dont include stderr output in stageroot variable

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch master:
https://git.openwrt.org/4ecef3f5c7cafdc1ce55a3cc40f74eaf702a2de2

commit 4ecef3f5c7cafdc1ce55a3cc40f74eaf702a2de2
Author: Petr Štetiar <ynezz at true.cz>
AuthorDate: Tue Sep 8 08:47:34 2020 +0200

    phase1: dont include stderr output in stageroot variable
    
    Otherwise it can result in strange error messages which are hard to
    debug.
    
    Ref: http://lists.openwrt.org/pipermail/openwrt-devel/2020-August/030826.html
    Signed-off-by: Petr Štetiar <ynezz at true.cz>
---
 phase1/master.cfg | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/phase1/master.cfg b/phase1/master.cfg
index edc4118..7186f5a 100644
--- a/phase1/master.cfg
+++ b/phase1/master.cfg
@@ -1019,7 +1019,8 @@ for target in targets:
 			property = "stageroot",
 			description = "Finding the rootfs staging directory",
 			command=["make", "--no-print-directory", "val.STAGING_DIR_ROOT"],
-			env = { 'TOPDIR': Interpolate("%(kw:cwd)s/build", cwd=GetCwd) }
+			env = { 'TOPDIR': Interpolate("%(kw:cwd)s/build", cwd=GetCwd) },
+			want_stderr = False
 		))
 
 		factory.addStep(ShellCommand(