The problem is that relying on the output of the 'ls' command is not
portable as its behavior is not the same between systems and it might
even not be available at all in (Windows).

So I added list_files that relies on the portable mysys library instead.
(and also list_files_write_file and list_files_append_file,
since the test was using '--exec ls' in that way.)

client/mysqltest.c:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  To be able to replace the use of '--exec ls' I have added
  list_files, list_files_write_file and list_files_append_file.
  
  list_files <dirname> [<filename incl. wild-cards>]
  is equivalent to 'ls <dirname>/[<filename incl. wild-cards>]'
  
  list_files_write_file creates/overwrites a file with the content
  list_files_append_file creates/appends a file with the content
  list_files* return a sorted output.
mysql-test/r/mysqltest.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  result file change, due to added test of the new list_files command.
mysql-test/suite/parts/inc/partition_check_drop.inc:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Using the new list_files instead of 'ls'.
  
  Changed the use of local variables (ls_file, file_list)
  and server variable (@aux).
mysql-test/suite/parts/inc/partition_layout.inc:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Using the new list_files instead of 'ls'.
mysql-test/suite/parts/inc/partition_layout_check1.inc:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Using the new list_files instead of 'ls'.
mysql-test/suite/parts/inc/partition_layout_check2.inc:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_alter1_1_2_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_alter1_1_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_alter1_2_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_alter2_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_alter3_innodb.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_alter3_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_basic_innodb.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_basic_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_basic_symlink_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_engine_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/suite/parts/r/partition_syntax_myisam.result:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Replaces '--exec ls' with list_files.
  Removal of the directory part of file listing.
mysql-test/t/mysqltest.test:
  Bug#35736 Test 'parts.partition_basic_symlink_myisam' depends on output of 'ls'
  
  Adding test for the new mysqltest commands list_files,
  list_files_write_file and list_files_append_file.