Problem: SHOW CREATE FUNCTION and SELECT DTD_IDENTIFIER FROM I_S.ROUTINES
returned wrong values in case of ENUM return data type and UCS2
character set.

Fix: the string to collect returned data type was incorrectly set to
"binary" character set, therefore UCS2 values where returned with
extra '\0' characters.
Setting string character set to creation_ctx->get_client_cs()
in sp_find_routine(), and to system_charset_info in sp_create_routine
fixes the problem.

Adding tests:
- the original test with Latin letters
- an extra test with non-Latin letters