Include python-file using the real path

When layout_config points to a symbolic link, Zuul attempted to load the
python function from directory of the symbolic link instead of the
parent of the link target.  That causes the scheduled to halt.

* Use realpath on layout_config path to make sure we will load from the
  proper place.
* Update documentation of python-file to mention the include is relative
  to the directory holding layout_config.

Change-Id: I33e221dd7c323423dbf781b53c06333dab2c7d29
Doc: ref links for "approval" requirement

The pipeline.require.approval logic is referenced at two other places
but lacks a link.  Add a label to easily browse to the approval
description.

Change-Id: Iba2e5a1db4023cd61444b2b8de53ffddfc03b16f
Document usage of yappi profiler

ff4eeec introduced support for yappi, a python profiler, which is used
when generating stack dumps (via SIGUSR2).  The commit forgot to update
the related documentation.

Change-Id: Iee1d680cf7b2df4c702666aaf778991c696c3274
Document that the "Stream Events" permission is needed.

Since Gerrit 2.7 the stream-events is only available to users
that are granted the "Stream Events" permission.

Change-Id: I38960b3647145043a31e5c948141831a84643753
Remove "properly" from error message for clarity

The tool is not checking to see that values of the variables are
"proper", it's only checking that they are set.

Removing the word "Proper" from the error message makes this clearer.

Change-Id: Ieea3565a05c8eeb6f67fd140a42197a059288f33
Merge "Doc: ref links for "approval" requirement"
Merge "Document that the "Stream Events" permission is needed."
Merge "Remove "properly" from error message for clarity"
Set gearman timeout to 300

In practice we are seeing that geard can occasionally get disrupted
and then temporarily backlogged enough that it exceeds the 30 second
timeout for submitting a job.  To make Zuul less fragile in this case,
increase the timeouts for any requests submitted to gearman.

Change-Id: I12741bb259c1a78fa2446d764318f84df34bac67
Merge "Include python-file using the real path"