Replace xrange across modules in networking-cisco repo

Use of xrange in n1kv_trunking_driver.py module is causing Jenkins to fail.

 pep8 runtests: commands[1] | flake8
2015-06-01 19:29:09.611 | /home/jenkins/workspace/gate-networking-cisco-pep8$ /home/jenkins/workspace/gate-networking-cisco-pep8/.tox/pep8/bin/flake8
2015-06-01 19:29:11.251 | ./networking_cisco/tests/unit/ml2/drivers/cisco/nexus/test_cisco_nexus.py:255:9: N325 Do not use xrange. Use range, or six.moves.range for large loops.
2015-06-01 19:29:11.251 | for idx in xrange(0, len(driver_result)):
2015-06-01 19:29:11.252 | ^
2015-06-01 19:29:11.252 | ./networking_cisco/tests/unit/ml2/drivers/cisco/nexus/test_cisco_nexus.py:793:9: N325 Do not use xrange. Use range, or six.moves.range for large loops.
2015-06-01 19:29:11.252 | for idx in xrange(0, len(driver_result)):
2015-06-01 19:29:11.252 | ^
2015-06-01 19:29:11.253 | ./networking_cisco/plugins/ml2/drivers/cisco/nexus/type_nexus_vxlan.py:173:13: N325 Do not use xrange. Use range, or six.moves.range for large loops.
2015-06-01 19:29:11.253 | vxlan_vnis |= set(xrange(tun_min, tun_max + 1))
2015-06-01 19:29:11.253 | ^
2015-06-01 19:29:11.254 | ./networking_cisco/plugins/cisco/cfg_agent/cfg_agent.py:291:9: N325 Do not use xrange. Use range, or six.moves.range for large loops.
2015-06-01 19:29:11.254 | for attempts in xrange(MAX_REGISTRATION_ATTEMPTS):
2015-06-01 19:29:11.254 | ^
2015-06-01 19:29:11.255 | ./networking_cisco/tests/unit/cisco/l3/test_l3_router_appliance_plugin.py:279:9: N325 Do not use xrange. Use range, or six.moves.range for large loops.
2015-06-01 19:29:11.255 | for attempts in xrange(max_attempts):
2015-06-01 19:29:11.256 | ^
2015-06-01 19:29:11.256 | ./networking_cisco/plugins/cisco/l3/plugging_drivers/n1kv_trunking_driver.py:198:17: N325 Do not use xrange. Use range, or six.moves.range for large loops.
2015-06-01 19:29:11.256 | for i in xrange(max_hosted):