[pitivi] build: Always set GST_PLUGIN_SYSTEM_PATH to /app/lib/gstreamer-1.0/

[Thibault Saunier <tsaunier src gnome org>]

commit 894cce2c0fd00b4c0cfed859ec0a08a634a49e78
Author: Thibault Saunier <tsaunier gnome org>
Date:   Sun Aug 14 18:01:05 2016 -0300

    build: Always set GST_PLUGIN_SYSTEM_PATH to /app/lib/gstreamer-1.0/
    
    And do not cd pitivi dir when entering the build env

 build/flatpak/pitivi-flatpak |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/build/flatpak/pitivi-flatpak b/build/flatpak/pitivi-flatpak
index d4df9a4..63d0b52 100755
--- a/build/flatpak/pitivi-flatpak
+++ b/build/flatpak/pitivi-flatpak
@@ -506,9 +506,9 @@ class PitiviFlatpak:  # pylint: disable=too-many-instance-attributes
                     "--env=CXX=ccache g++"]
 
         for envvar in [
-                "GST_PLUGIN_SYSTEM_PATH", "GST_CHECKS", "GST_DEBUG",
-                "GST_PLUGIN_SYSTEM_PATH", "GST_VALIDATE", "GST_VALIDATE_LAUNCHER_DEBUG",
+                "GST_CHECKS", "GST_DEBUG", "GST_VALIDATE", "GST_VALIDATE_LAUNCHER_DEBUG",
                 "PITIVI_DEBUG", "PITIVI_DEVELOPMENT", "DISPLAY", "GST_DEBUG_DUMP_DOT_DIR",
+                ("GST_PLUGIN_SYSTEM_PATH", "/app/lib/gstreamer-1.0/"),
                 ("GST_PRESET_PATH",
                  "/app/share/gstreamer-1.0/presets/:/app/share/pitivi/gstpresets/"),
                 ("GST_ENCODING_TARGET_PATH",