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

[ctubbsii]

We can drop the user and password options, as the user can specify these in a client config file, and that's not what this example is trying to teach, so it's fine to omit them. I would not expand the execute-command, as it's much more common for people to use the single letter version.

[ctubbsii]

This README is already in the directory, so the cd is implied. This part doesn't really need to change, does it?