Command updates for dirlist, helloworld, isolation, and sample examples

[Amemeda]

dirlist:

• updated instructions at the beginning specifying NOT to delete tables dirTable, dataTable, and indexTable until after the dirlist example AND filedata example are completed. Added as the instrutions say you can delete after finishing dirlist, but once you get to filedata, it uses some data from the ingest in dirlist example, and if the tables were deleted, an ingest will have to be run again.
• updated "$ accumulo shell -u root -e 'setauths -u username -s exampleVis'" to
  "$ accumulo shell -u root -e 'setauths -u root -s exampleVis'"

helloworld:

• updated "To view the entries, use the shell (run accumulo shell -u username -p password to access it) to scan the table:" to "To view the entries, use the shell (run accumulo shell --user root --password secret to access it) to scan the table:"

isolation:

• updated "$ accumulo shell -u -p -e 'createnamespace examples' " to
  "$ accumulo shell --user root --password secret --execute-command 'createnamespace examples' "

sample:

• added expected second file output from rfile-info command, updated formatting of output
• updated "accumulo rfile-info" to "accumulo file rfile-info"
• updated rfile-info command

[DomGarguilo]

Your changes look good! I went through the examples using your updated instructions and updated a few adjacent things while I was doing that.