Install toolchain using --sysroot.

install_toolchain no longer supports --board. This CL converts
cros_generate_sysroot and generate_delta_sysroot to using --sysroot.

BUG=brillo:662
TEST=trybot run on daisy-paladin (tests ChromeSDK).
TEST=unittests.

CQ-DEPEND=CL:262220

Change-Id: Ic29ef4b140fecc163861fb678e93fe80337c077a
Reviewed-on: https://chromium-review.googlesource.com/262209
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Trybot-Ready: Bertrand Simonnet <bsimonnet@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
diff --git a/scripts/cros_generate_sysroot.py b/scripts/cros_generate_sysroot.py
index bd48d7a..83e4db0 100644
--- a/scripts/cros_generate_sysroot.py
+++ b/scripts/cros_generate_sysroot.py
@@ -74,8 +74,7 @@
     sysroot_lib.WriteSysrootConfig(self.sysroot, config)
     cros_build_lib.RunCommand(
         [os.path.join(constants.CROSUTILS_DIR, 'install_toolchain'),
-         '--noconfigure', '--board_root', self.sysroot, '--board',
-         self.options.board])
+         '--noconfigure', '--sysroot', self.sysroot])
 
   def _InstallKernelHeaders(self):
     self._Emerge('sys-kernel/linux-headers')