selinux: create a transition type for module loading

selinux: create a transition type for module loading

Defines a type 'openvswitch_load_module_t' used exclusively for loading
modules.  This means that the 'openvswitch_t' domain won't require
access to the module loading facility - such access can only happen
after transitioning through the 'openvswitch_load_module_exec_t'
transition context.

A future commit will instruct the selinux policy on how to label the
appropriate script with extended attributes to make use of this new domain.

Acked-by: Ansis Atteka <aatteka@ovn.org>
Acked-by: Timothy Redaelli <tredaelli@redhat.com>
Signed-off-by: Aaron Conole <aconole@redhat.com>