common/ase/configuration_change_tftp.1.1.py does not sanitize tftp_config_file_name_prefix

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Script common/ase/configuration_change_tftp.1.1.py does not sanitize tftp_config_file_name_prefix parameter.

If the parameter contains blank space (" ") for example it will fail because line 223 :
tftp_command = 'copy running-config tftp://%s/%s %s' % (tftp_server,
file_name,
tftp_format)
will generate an invalid command (copy run tftp://server/illegal file json) for example.
an easy fix is to sanitize the parameter with re()
sanitized_file_name_prefix = sub('[^A-Za-z0-9]','_',file_name_prefix )