add sources controller.
1120671 - missing operation from reaper and monthly tasks

I also added documentation about these tasks
add last_unit_added and last_unit_removed to repo docs
use serializer.
Added a scheduling task for reaper and monthly

Also added a couple of unit tests to make sure that the schedling
task actually calls the apply_async for the task that does the work
add get single content source.
add python-mongoengine to deps (el7 only)

This commit adds python-mongoengine for el7 builds. An EL6 version is already
available via EPEL.
add unit tests.
Merge pull request #1220 from pulp/barnabycourt-doc-unit-add-remove-timestamps

add last_unit_added and last_unit_removed to repo docs
Fixed method names and added stronger assertion to unit tests
setting a max DB connect timeout of 1 second for pulp-manage-db

If a user runs pulp-manage-db while mongo is not listening for connections,
that user does not want the usual retry back-off. They want pulp-manage-db to
keep trying about once per second until a connection is established.
Automatic commit of package [pulp] release [2.4.2-0.1.beta].
Automatic commit of package [pulp-nodes] release [2.4.2-0.1.beta].
Merge remote-tracking branch 'origin/2.4-testing' into 2.4-dev

Conflicts:
	pulp.spec
Automatic commit of package [pulp] release [2.5.0-0.8.beta].
Automatic commit of package [pulp-nodes] release [2.5.0-0.8.beta].
Merge remote-tracking branch 'origin/2.5-testing' into 2.5-dev
add binding tests.
Merge remote-tracking branch 'origin/2.4-dev' into 2.5-testing

Conflicts:
	nodes/pulp-nodes.spec
	pulp.spec
	rel-eng/packages/pulp
	rel-eng/packages/pulp-nodes
Merge remote-tracking branch 'origin/2.5-testing' into 2.5-dev