Implementing string representation for model classes

We want to have meaningfull representation. This is
useful when we debug and want to see the actual
attributes of the object. The current __repr__
of those classes is the default python implementation
 and does not provide
information about the object attributes.
Solve Bug #1084231

Change-Id: I1ea5d741d2fd2da13712e0d51d2c73dfba4991cf
Solve the conflict below:
Conflicts:
	quantum/tests/unit/test_db_plugin.py
Ensures that the dnsmasq configuration file flag is always set

Fixes bug 1094183

If the flag is not set then the default configuration file may
be used. This may be problematic in certain setups.

Change-Id: Ibd0be960779f391a198454510dd6edcbc69c149c
Merge "Ensures that the dnsmasq configuration file flag is always set"
Merge "Implementing string representation for model classes"