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 <username> --password <password> -e

terasort:

• updated usages of -u root -p secret -e to --user <username> --password <password> -e

uniquecols:

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

Omitted all username/password references from --user --password commands for consistency across code.