Fix security group list when not defined for an instance

If an instance has an empty security group list an exception
is thrown due to iteration attempt of None.

To fix this, this patch modifies get_instance_security_group
to return an empty list instead of None.

Change-Id: I7efb3c3a58d7e20501d126c6d194479ca1d14166
Closes-Bug: #1291489
(cherry picked from commit c32986966dfd034c3d706b2e9ab2820a2c3cfc3e)
VMware: use default values in get_info() when properties are missing

The properties that we retrieve from VirtualMachineConfigSummary are
optional ('summary.config.numCpu', 'summary.config.memorySizeMB') and
if they are missing we should return default values from get_info()

This patch also improves the unit test for get_info(). It removes the
test in test_driver_api.py (test_get_info() and test_spawn() are the
same) and adds a new test in test_vmops.py

Conflicts:

	nova/tests/virt/vmwareapi/test_driver_api.py
	nova/tests/virt/vmwareapi/test_vmops.py

Closes-Bug: 1317912
Change-Id: Ibbb28985d13de371fdac8a119ad820d25acc21be
(cherry picked from commit 2db7528ca258d7b0c1205ab2f9a76569d9f9a82d)
Merge "Fix security group list when not defined for an instance" into stable/icehouse
Merge "VMware: use default values in get_info() when properties are missing" into stable/icehouse