Fix the pgrep/pkill -j testcases (DO NOT MERGE -- merely for review/illustration)

The attached patch does the following things:

1. Refactors/simplifies the root user check.
2. Uses the long parameter names for the jail command.
3. Uses a temporary directory for the jail to avoid having multiple jails stomp over one another.
4. Looks up the jail by name and jid instead of 
5. Look up the exact arguments list when doing the search to avoid looking for the jail command instead of look for the sleep command being run in the jail.
6. Use ps -J for looking up the process being run in the jail to avoid finding processes outside the jail with pgrep -j any, etc.
7. Add a trap to cleanup jails created when the testcases were run.

Testing done:

<pre>
# prove -rv *j*
pgrep-j_test ..
1..3
ok 1 - pgrep -j <jid>
ok 2 - pgrep -j any
ok 3 - pgrep -j none
ok
pkill-j_test ..
1..3
jail: /usr/tests/bin/pkill/pkill-j_test.hnIn3IY/sleep.txt 5: exited on signal 15
kill: 22781: No such process
ok 1 - pkill -j <jid>
jail: /usr/tests/bin/pkill/pkill-j_test.hnIn3IY/sleep.txt 5: exited on signal 15
jail: /usr/tests/bin/pkill/pkill-j_test.hnIn3IY/sleep.txt 5: exited on signal 15
kill: 22793: No such process
kill: 22794: No such process
ok 2 - pkill -j any
kill: 22802: No such process
ok 3 - pkill -j none
jail: "pkill-j_test_1-2" not found
jail: "pkill-j_test_3" not found
ok
All tests successful.
Files=2, Tests=6, 44 wallclock secs ( 0.07 usr  0.02 sys +  0.02 cusr  0.23 csys =  0.34 CPU)
Result: PASS
</pre>

Sponsored-by: EMC / Isilon Storage Division