Msf::Session::Scriptable compatibility

MSP-9228

Update methods to use Metasploit::Framework.pathnames and
Msf::Fraemwork#pathnames.  Use module cache to access post modules for
tab completion.  Spec changes to tab completion and
Msf::Session::Scriptable.  Changes to cmd_sessions is unspeccable at
this time because the method is too complex.