Closes #773

Without pid, wait always return 0.

This change tracks pids to ensure we have the return code
of the background jobs.

Travis ressources for opensource project is limited

This change will limit the number of jobs per PR in parallel, allowing
more PR to be processed at the same time.

And remove the build of the image of each commit (save 3-4 minutes).
It pulls the image from dockerhub (I will create a new repo to have
this image updated automatically).

It's run in parallel tests of differents storage system.

The overall time of testing is still ~40 minutes, but now we use only 3
jobs instead of 10.

This change adds a redis driver and uses it by default in devstack.
Because reading/writting from/to disks is too slow in our testing
environment.

Change-Id: If617260a9d8e38dc9ba9311c832be333346dd41e

Change-Id: I4ec57a2ff3057ee2fe3ac49cab66cfe8628ab2d6

This relies on s3rver to test (via pifpaf), but also has been tested
against AWS S3 and works perfectly.

Change-Id: I99d6394f662fdecd4021990aa3377516bebff674

The rados module was mocked because it was not possible to easy ceph
into gate. But now pifpaf support it and we can install anything we want
with bindeps.txt file.

Also future changes will use more and more API from Ceph, making Rados mock class
more hard to maintain.

This change removes the mock and uses a real ceph cluster setuped with
pifpaf to run tests.

Change-Id: I50bd1cac0017565ef678c2ce9235a21368eeea93

It's utopic to think the user is going to write a mysql+pymysql:// URL
by default. Let's do that for them.

Change-Id: I00f050423fd86ffd51d7ef2bb7f5e5928620f412

Change-Id: Iaf046e48ec4331911f5a142f82e26667a0ca8e37

Change-Id: I699c8632aaa2cb833cfa066783faf1ed3d830194

When running a specific env such as e.g. py27-postgresql-file, the lines
in the global commands variable starting with "py27:" also matches,
which means we ended up running the global test suite too!

This refactor the code a bit so we always call run-tests.sh with just
some environment variable set using `setenv'.

Change-Id: Icb2879f383c1d0a09a1cd1fce1cbadfa1207c6c9

We now rely on different tox targets to speed standard test run and have
more parrelism.

Depends-On: I56f1988a7f8ad593713203187559e2654b0c2fb2
Change-Id: I5ddb00a53016f01fcd49a6681a449e9b2deeaf7d

Change-Id: Ief184f7f2cae67a9617f4803a5f629067538f44a

Change-Id: I418de2e0587114f9181fdda8f17518b2c43557a4