Test: more fix to 038.pcp_commands regression test.

Test: more fix to 038.pcp_commands regression test.

Commit 04e09df17 was not enough fix. The test calls pcp_proc_info()
pgpool_adm function along with user name and password (in the test
password is the same string as user name). Problem is, the user name
is obtained from a user name that runs the test, and we use psql -a to
submit the SQL, which prints the user name. Of course the user name
can vary depending on the environment, and it makes the test fail.  To
fix the issue, run psql without -a option.