We ran into a RuntimeError yesterday on this line, the callback can
modify this dict and make the iteration raise an error. Using keys
method to iterate is safer.
See
http://stackoverflow.com/questions/11941817/python-runtimeerror-dictionary-changed-size-during-iteration-how-to-avoid-th/11941855#11941855

This is needed to get the tests working on environments where zmq was
not initalizated.

The environment variable XDG_CONFIG_HOME is set to get the leap
configuration in the temp folder.

Before this commit, protobuf and protobuf.socketrpc were used to serialize and
transmit messages between events clients. This change implements a simpler ZMQ
client/server events mechanism that uses ZMQ sockets for transmitting messages
from clients to server and to redistribute such messages to subscribed
clients.

Closes: #6359

Implements an HTTP client the twisted way, with a focus on pinning the
SSL certs.

* Related: #6506

The certificate validity times were converted to local time and later on
compared with UTC time, which caused the certificate not being updated
at the right times.
Add tests to be sure this is not happenning again.
Add a joint pem file for the existing cert and key files to ease test.

- Resolves: #6994

In some systems the used tmp dir is like '/tmp/leap_tests-asdf' and in
others is like '/tmp/username/leap_tests-asdf'.
With this fix we protect the home dir and consider different possible
temp directories.

Using trial there is no setUpClass neither tearDownClass, the setting up
of the environment needs to be in an external class to be able to call
it from inhereted classes.