Remove DHCP lease logic

Previously neutron was keeping track of dhcp lease time in order
to ensure it didn't hand out an ip address that was already leased.
This patch removes that logic and instead leverages the dhcp_release
utility. This allows us to reuse ip addresses immediately after a port
is deleted. This patch also bumps the lease time to 24 hours instead
of 2 minutes with reduces the amount of dhcp traffic.

DocImpact

There is a DocImpact for this bug related to the upgrade path. One should
first upgrade their dhcp-agents. Then wait till the dhcp_lease time has
expired. Lastly, update neutron-server in order to avoid the case where
an instance is deleted and the dnsmasq process has not released the lease
and neturon allocates that ip to a new port.

Fixes bug: 1202392
Implements blueprint: remove-dhcp-lease

Change-Id: Ifcb4f093c92904ceb896438987d53e692eb7fb26
Signed-off-by: Christoph Thiel <c.thiel@telekom.de>

Conflicts:
	etc/quantum/rootwrap.d/dhcp.filters
	quantum/agent/dhcp_agent.py
	quantum/agent/linux/dhcp.py
	quantum/common/config.py
	quantum/db/db_base_plugin_v2.py
	quantum/db/dhcp_rpc_base.py
	quantum/tests/unit/test_db_plugin.py
	quantum/tests/unit/test_dhcp_agent.py
	quantum/tests/unit/test_linux_dhcp.py
	setup.cfg
Fix testcase 'test_create_subnet_with_two_host_routes' failed

Fix bug 1179348

Change-Id: I0cd5d303da0f394cec173aeee52efcd337282c94
Signed-off-by: Christoph Thiel <c.thiel@telekom.de>
Fix testcase 'TestPortsV2.test_range_allocation' failed randomly

Fix bug 1179370

Change-Id: Id5645546c98549c9d7cf68359e0f6fa128ad84b7
Signed-off-by: Christoph Thiel <c.thiel@telekom.de>