Update FeatureTests to use the same libvirt connection used by Model

The former code was running the FeatureTests with the system libvirt
connection, so if a developer used Model() with a different
libvirt URI the feature tests would report a false positive result.
To avoid this problem share the libvirt connection used by Model() with
FeatureTests.

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>
Set domain type in FeatureTests according libvirt URI

When using the libvirt URI 'test:///default' the domain type must be
'test' instead of 'kvm'

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>
Move featuretests.py to /model

FeatureTests is only used by Model() as it tests the libvirt and qemu
capabilities. So move it to /model

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>