Add tesing deps installation into hacking/README

Signed-off-by: Max Riveiro <kavu13@gmail.com>
Fix ValueError when selection contains a colon
Remove print statements

"print item" raises an exception when type of item is
jinja2.runtime.StrictUndefined
Add missing sha1 import on known_hosts.py
Adding type int for count (in line with other cloud modules)
Acclerate improvements

* Added capability to support multiple keys, so clients from different
  machines can connect to a single daemon instance
* Any activity on the daemon will cause the timeout to extend, so that the
  daemon must be idle for the full number of minutes before it will auto-
  shutdown
* Various other small fixes to remove some redundancy

Fixes #5171
Documentation updates for accelerate mode improvements
Adding in a configurable option for the accelerate daemon timeout

This was apparently an oversite, as it has never been configurable
despite having a module parameter for the timeout.
Merge pull request #6634 from pilou-/fix

Remove print statements
Merge pull request #6635 from pilou-/debconf

Fix ValueError when selection contains a colon
Merge pull request #6639 from fvieira/devel

Add missing sha1 import on known_hosts.py
Merge pull request #6640 from falloutdurham/ec2_count

ec2: Adding type int for count (in line with other cloud modules)
Merge pull request #6631 from kavu/add_testing_deps_to_hacking_readme

Add tesing deps installation into hacking/README
adds missing `'` to debconf examples
Update CONTRIBUTING.md

Some clarifications about workflow and the priority queue in GitHub
Merge pull request #6642 from sethwoodworth/patch-1

[docs] adds missing `'` to debconf examples