Change to pg_test_fsync output

I propose the attached patch to change pg_test_fsync's output from
"microsecs" to "usecs", which is the designation we use in other places.
Also remove parentheses, e.g.

         1 * 16kB open_sync write        8012.933 ops/sec     125 usecs/op
         2 *  8kB open_sync writes       5399.901 ops/sec     185 usecs/op
         4 *  4kB open_sync writes       3340.958 ops/sec     299 usecs/op
         8 *  2kB open_sync writes       1903.621 ops/sec     525 usecs/op
        16 *  1kB open_sync writes       1032.606 ops/sec     968 usecs/op

This is new output for 9.3.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +