ZTS: fix "not found" errors

ZTS: fix "not found" errors

This commit fixes several "not found" errors caused by calling undefined
or incorrect shell functions in the following ZFS Test Suite groups:

   * alloc_class
   * channel_program/lua_core
   * channel_program/synctask_core
   * cli_root/zpool_import
   * cli_user/misc

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed-by: bunder2015 <omfgbunder@gmail.com>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #8152