ctdb-scripts: Update script boilerplate to avoid shellcheck warnings

ctdb-scripts: Update script boilerplate to avoid shellcheck warnings

* Assign the output of dirname to temporary variable to avoid word
  splitting when directory name contains whitespace

* Drop export of CTDB_BASE to avoid masking broken return value -
  functions file does the export anyway

* Quote path when including functions file

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>