Msf::Framework#pathnames

MSP-9228

Use an instance of Metasploit::Framework::Framework::Pathnames for
Msf::Framework#pathnames.  Msf::Framework#pathnames has not writer and
:pathnames must be passed to #initialize.  This is to prevent sharing of
mutable state between threads and because in the normal use cases the
Metasploit::Framework::Framwork::Pathnames#root is only changed once in
the beginning by command line options.