Changed influxdb v2 storage option 'cacert' to 'cafile'
Changed influxdb v2 storage option 'cacert' to 'cafile'

In order to respect consistency across the whole project,
'cacert' option as defined in the influxdb v2 storage
has been changed to 'cafile'.
(as it is already the case for e.g. Gnocchi collector)

Change-Id: Idb4a39d7ad9edf0f3eecb32b7d4e4e34ebe73a81

openstack/cloudkitty,stackforge/cloudkitty,openstack/cloudkitty,stackforge/cloudkitty