[autotest] Drop uses of CrosHost._get_board_from_afe

BUG=chromium:678430
TEST=unittests

Change-Id: I1df262a0f600a791c0c35326b1b459cd931eded3
Reviewed-on: https://chromium-review.googlesource.com/439890
Commit-Ready: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@google.com>
diff --git a/server/hosts/cros_firmware.py b/server/hosts/cros_firmware.py
index 1c43b6a..41c2eda 100644
--- a/server/hosts/cros_firmware.py
+++ b/server/hosts/cros_firmware.py
@@ -256,8 +256,13 @@
         if not _is_firmware_update_supported(host):
             return
         # Test 2 - The DUT has an assigned stable firmware version.
-        stable_firmware = afe_utils.get_stable_firmware_version(
-                host._get_board_from_afe())
+        info = host.host_info_store.get()
+        if info.board is None:
+            raise hosts.AutoservVerifyError(
+                    'Can not verify firmware version. '
+                    'No board label value found')
+
+        stable_firmware = afe_utils.get_stable_firmware_version(info.board)
         if stable_firmware is None:
             # This DUT doesn't have a firmware update target
             return
diff --git a/server/hosts/cros_host.py b/server/hosts/cros_host.py
index 6de91ef..2f420d8 100644
--- a/server/hosts/cros_host.py
+++ b/server/hosts/cros_host.py
@@ -331,8 +331,12 @@
 
 
     def _get_cros_repair_image_name(self):
-        return afe_utils.get_stable_cros_image_name(
-                self._get_board_from_afe())
+        info = self.host_info_store.get()
+        if info.board is None:
+            raise error.AutoservError('Cannot obtain repair image name. '
+                                      'No board label value found')
+
+        return afe_utils.get_stable_cros_image_name(info.board)
 
 
     def verify_job_repo_url(self, tag=''):