Support parsing dir keywords

[jw3]

 dir         If you wish to match a directory, then use this by giving the full path to the directory. Its recommended to
                          end with the / to ensure it matches a directory. There are 3 keywords  that  dir  supports:  execdirs,  sys‐
                          temdirs, untrusted.

                          execdirs    The execdirs option will match against the following list of directories:

                                      /usr/       /bin/ /sbin/ /lib/ /lib64/ /usr/libexec/

                          systemdirs  The systemdirs option will match against the same list as execdirs but also includes /etc/.

                          untrusted   The  untrusted option will look up the current executable's full path in the rpm database to see
                                      if the executable is known to the system. The rule will trigger if the file in question  is  not
                                      in  the  trust database. This option is deprecated in favor of using obj_trust with execute per‐
                                      mission when writing rules.