[pitivi] validate: Show more info when gst-validate-launcher missing

[Alexandru Băluț <alexbalut src gnome org>]

commit 933ac9759f7e6499aee66b71f52f37fd07d2e7c9
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Tue Oct 25 17:20:49 2016 +0200

    validate: Show more info when gst-validate-launcher missing
    
    Used "which" instead of running the command directly because it prints
    the PATH in which it searched.
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D1428

 tests/validate-tests/runtests |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
---
diff --git a/tests/validate-tests/runtests b/tests/validate-tests/runtests
index cbd2a03..e42fb65 100755
--- a/tests/validate-tests/runtests
+++ b/tests/validate-tests/runtests
@@ -8,9 +8,12 @@ import sys
 
 GST_VALIDATE_LAUNCHER_COMMAND = "gst-validate-launcher"
 
-if (os.system(GST_VALIDATE_LAUNCHER_COMMAND + " -h > %s 2>&1" % os.devnull) != 0):
-    print("Make sure to install gst-validate: 
http://cgit.freedesktop.org/gstreamer/gst-devtools/tree/validate/";
-          " before running the testsuite")
+try:
+    subprocess.check_call("which %s" % GST_VALIDATE_LAUNCHER_COMMAND, shell=True)
+except subprocess.CalledProcessError as e:
+    print("ERROR: Cannot find %s: %s" % (GST_VALIDATE_LAUNCHER_COMMAND, e))
+    print("Make sure to install gst-devtools:")
+    print("    http://cgit.freedesktop.org/gstreamer/gst-devtools/tree/validate/";)
     sys.exit(127)
 
 path = os.path.abspath(os.path.join(os.path.dirname(__file__)))  # pylint: disable=invalid-name