Updating commands in spark, reservations, terasort, and uniquecols examples

[Amemeda]

reservations:

• "$ /path/to/accumulo org.apache.accumulo.server.util.ListInstances" updated to "$ accumulo inst list-instances"
• updated usages of "-u root -p secret -e" to "--user root --password secret --execute-command"

terasort:

• updated usages of "-u root -p secret -e" to "--user root --password secret --execute-command"

uniquecols:

• updated "$ /path/to/accumulo shell -u username -p secret" to "$ accumulo shell --user root --password secret"
• updated multiple references of "examples" table that was misspelled as "example"

spark:

• updated instructions specifying user to be in spark directory before running run.sh batch