Description of problem:
targetcli crashes when creating a block-based backstore.

Version-Release number of selected component (if applicable):
targetcli-2.1.fb48-3.fc28.noarch

How reproducible:
easy

Steps to Reproduce:
/> cd backstores/block
/backstores/block> create block_backend1 /dev/sdb


Actual results:

Traceback (most recent call last):
  File "/usr/bin/targetcli", line 122, in <module>
    main()
  File "/usr/bin/targetcli", line 112, in main
    shell.run_interactive()
  File "/usr/lib/python3.6/site-packages/configshell_fb/shell.py", line 905, in run_interactive
    self._cli_loop()
  File "/usr/lib/python3.6/site-packages/configshell_fb/shell.py", line 734, in _cli_loop
    self.run_cmdline(cmdline)
  File "/usr/lib/python3.6/site-packages/configshell_fb/shell.py", line 848, in run_cmdline
    self._execute_command(path, command, pparams, kparams)
  File "/usr/lib/python3.6/site-packages/configshell_fb/shell.py", line 823, in _execute_command
    result = target.execute_command(command, pparams, kparams)
  File "/usr/lib/python3.6/site-packages/configshell_fb/node.py", line 1406, in execute_command
    return method(*pparams, **kparams)
  File "/usr/lib/python3.6/site-packages/targetcli/ui_backstore.py", line 561, in ui_command_create
    readonly = self._ui_block_ro_check(dev)
  File "/usr/lib/python3.6/site-packages/targetcli/ui_backstore.py", line 539, in _ui_block_ro_check
    buf = array.array('c', [chr(0)] * 4)
ValueError: bad typecode (must be b, B, u, h, H, i, I, l, L, q, Q, f or d)


Expected results:

/backstores/block> create block_backend1 /dev/sdb
Created block storage object block_backend1 using /dev/sdb.

Additional info:

Fixed by
https://github.com/open-iscsi/targetcli-fb/commit/ed5ff9b9505e50b545e86dfbdd32077f0ddda0cb?diff=unified