Unit test explain_filename is unstable

[Laurynas Biveinis]

E.g. on 5.5:

unit_tests w0 [ fail ]
        Test ended at 2016-08-01 02:19:20

ctest failed with exit code 2048, see result below

--------------------------------------------------------------------------
Test project /mnt/workspace/percona-server-5.5-param/BUILD_TYPE/debug/Host/ubuntu-trusty-64bit
      Start 1: pfs_instr_class
 1/14 Test #1: pfs_instr_class .................. Passed 0.00 sec
      Start 2: pfs_instr_class-oom
 2/14 Test #2: pfs_instr_class-oom .............. Passed 0.00 sec
      Start 3: pfs_instr
 3/14 Test #3: pfs_instr ........................ Passed 0.00 sec
      Start 4: pfs_instr-oom
 4/14 Test #4: pfs_instr-oom .................... Passed 0.00 sec
      Start 5: pfs
 5/14 Test #5: pfs .............................. Passed 0.59 sec
      Start 6: bitmap
 6/14 Test #6: bitmap ........................... Passed 1.77 sec
      Start 7: base64
 7/14 Test #7: base64 ........................... Passed 0.02 sec
      Start 8: my_vsnprintf
 8/14 Test #8: my_vsnprintf ..................... Passed 0.00 sec
      Start 9: my_atomic
 9/14 Test #9: my_atomic ........................ Passed 2.02 sec
      Start 10: my_rdtsc
10/14 Test #10: my_rdtsc ......................... Passed 0.13 sec
      Start 11: lf
11/14 Test #11: lf ............................... Passed 2.10 sec
      Start 12: my_malloc
12/14 Test #12: my_malloc ........................ Passed 0.00 sec
      Start 13: explain_filename
13/14 Test #13: explain_filename .................***Failed 0.00 sec
      Start 14: my_decimal
14/14 Test #14: my_decimal ....................... Passed 0.00 sec

93% tests passed, 1 tests failed out of 14

Total Test time (real) = 6.66 sec

The following tests FAILED:
  13 - explain_filename (Failed)
Errors while running CTest

This could be caused by interaction with libeatmydata.

[Laurynas Biveinis (laurynas-biveinis)]

     https://github.com/percona/percona-server/pull/755
     https://github.com/percona/percona-server/pull/756
     https://github.com/percona/percona-server/pull/757

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-3501