validate-transcoding: Dot pipeline on error
scenario: Add support for "config" actions, actions executed at parse time

This type of actions is used to change some parametter on GStreamer
core and it plugins, it can be fore example, to change the rank of a
plugin or things like that.
scenario: Add a "set-feature-rank" config action

This action can be used to change the rank of a particular element,
so you can force a particular element to be used when using
autoplugging elements (such as decodebin, encodebin, and friends)
scenario: Do not execute anything when listing scenarios
tools: Simplify the setting of action scenario vs config scenario

This make it easier for user to understand the difference between
the two concepts and avoids confusion.

Change-Id: Ib42913722c93a1e7e3c8b156173c458230946592

Conflicts:
	validate/tools/gst-validate-transcoding.c
	validate/tools/gst-validate.c
pad-monitor: Do not concider TIME_NONE as 0 for serialized events

In case we have serialized events right after a buffer that had no
timestamp set we concider that last timestamp was 0, but we can
actually not concider the timestamp at all in that case as it is
only "meaningless value".
tools: transcoding: Avoid reencoding unless explicitely specified
validate-scenarios: list scenarios in GST_VALIDATE_SCENARIOS_PATH

GST_VALIDATE_SCENARIOS_PATH was used only for loading scenarios,
so any in that path would not be listed by -l.

Change-Id: If3cb94867ef3876933bda02477675c8ccf67baaf
validate: fix installation

* install headers
* fix libname in pk file
Add a test launcher tool
validate: drop unneeded stdio include
validate: fix parallel build

Without this, parallel building with > 2 jobs fails.
Also, LDFLAGS should not contain -l flags but _LIBADD.
validate: tools: Cleanup test launcher tool

Previous commit was not meant to be pushed and those two should have
been fixed up together, sorry for the mistake
validate: tools: media-info: Fixes in the media file descriptor parsing code

We used to always fail when the user was passing something not NULL as err
validate: tools: Add a gst-validate test manager
validate: tools: Unref the pipeline before the runner and monitor

Avoids segfault in some cases, and monitors and runners have week ref on
their targets.
validate: launcher: add the debug logger from pitivi

It is way more powerfull, simple to use and usefull
than the stock python one and has been proved to work reliably
validate: tools: Refactor and add a GstValidateTranscodeTest class
validate: tools: Concider timeouts as errors when printing tests
validate: tools: Enhance error message for GstValidate tests