Improve the fifo open timeout error message in `android_shell.py`.

See https://github.com/domokit/devtools/issues/56.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/1505783002 .

Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: 293bcf7659e2d2f4ef786be688fb109a3eed3af1

devtoolslib/android_shell.py

diff --git a/devtoolslib/android_shell.py b/devtoolslib/android_shell.py
index 178934a..dfa0c84 100644
--- a/devtoolslib/android_shell.py
+++ b/devtoolslib/android_shell.py
@@ -126,7 +126,7 @@
           time.sleep(1)
         if on_fifo_closed:
           on_fifo_closed()
-        raise Exception('Unable to find fifo.')
+        raise Exception('Timed out waiting for shell the create the fifo file.')
       _wait_for_fifo()
       stdout_cat = subprocess.Popen(
           self._adb_command(['shell', 'run-as', _MOJO_SHELL_PACKAGE_NAME,