Fix smoke test to not hard-code python executable location.

BUG=670678

Change-Id: If3104a6d666e84d7150ba805672dac3e34a1f9a1
Reviewed-on: https://chromium-review.googlesource.com/416269
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>

tests/gclient_smoketest.py

@@ -499,9 +499,9 @@ class GClientSmokeGIT(GClientSmokeBase):
         ('running', self.root_dir),                 # pre-deps hook
         ('running', self.root_dir),                 # pre-deps hook (fails)
     ]
-    expected_stderr = ("Error: Command '/usr/bin/python -c import sys; "
+    expected_stderr = ("Error: Command '%s -c import sys; "
                        "sys.exit(1)' returned non-zero exit status 1 in %s\n"
-                       % self.root_dir)
+                       % (sys.executable, self.root_dir))
     stdout, stderr, retcode = self.gclient(['sync', '--deps', 'mac', '--jobs=1',
                                             '--revision',
                                             'src@' + self.githash('repo_5', 3)])