gooftool: fix 'HasFpmcu()'

This CL fix a bug in HasFpmcu that it always thinks the FPMCU exists.
Also add a unittest to assert this won't be break in the future.

BUG=b:141172626
TEST=make test
TEST=run pylint: ignore 'xrange' error, it will be fixed in CL:1868791

Change-Id: I77dffd9d5fbeb6b3465118fee3cbbd0e8e0b4f1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/factory/+/1925927
Tested-by: Wei-Han Chen <stimim@chromium.org>
Tested-by: Fei Shao <fshao@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Philip Chen <philipchen@chromium.org>
Commit-Queue: Fei Shao <fshao@chromium.org>
diff --git a/py/gooftool/commands.py b/py/gooftool/commands.py
index 2325eaa..f557893 100755
--- a/py/gooftool/commands.py
+++ b/py/gooftool/commands.py
@@ -81,7 +81,7 @@
     FPMCU_PATH = '/dev/cros_fp'
     has_fpmcu_path = os.path.exists(FPMCU_PATH)
     has_cros_config_fpmcu = False
-    if Shell(['cros_config', '/fingerprint', 'board']):
+    if Shell(['cros_config', '/fingerprint', 'board']).success:
       has_cros_config_fpmcu = True
 
     if has_fpmcu_path is False and has_cros_config_fpmcu is True: