Fixed the test code to handle the background job properly (#228)

Since the test code only uses "sleep" to wait for the background job
to finish, an incomplete background job could cause the next test to fail. 

As an example, we have confirmed that the test fails on a poorly 
performing server.

sql/show.sh

@@ -86,15 +86,15 @@ echo ''
 echo '###### SHOW COMMAND TEST-0002 ######'
 echo '###### Status RUNNING  ######'
 init_catalog
-pg_rman backup -B ${BACKUP_PATH} -b full -Z -p ${TEST_PGPORT} -d postgres --quiet &
+pg_rman backup -B ${BACKUP_PATH} -b full -Z -p ${TEST_PGPORT} -d postgres --quiet & # run in background
 sleep 1
 pg_rman show -B ${BACKUP_PATH} > ${TEST_BASE}/TEST-0002-show.out 2>&1
 if grep "RUNNING" ${TEST_BASE}/TEST-0002-show.out > /dev/null ; then
      echo 'OK: RUNNING status is shown properly.'
 else
      echo 'NG: RUNNING status is not shown.'
 fi
-sleep 5
+wait # wait to finish the backup running in the background with '&'.
 echo ''
 
 echo '###### SHOW COMMAND TEST-0003 ######'