tkey-gssapi-credential option in /etc/named.conf creates a memory leak

Issue

Valgrind reports memory leak if "tkey-gssapi-credential" is used in /etc/named.conf.

Steps to Reproduce:
- Configure tkey-gssapi-credential (e.g. default IPA install with integrated DNS)
- Run named under valgrind

E.g.:
$ export KRB5_KTNAME=/etc/named.keytab
$ valgrind --leak-check=full named -g -u named

• Let named to start and then terminate it with CTRL+C or rndc stop

Actual results:

==10844== 63 (16 direct, 47 indirect) bytes in 1 blocks are definitely lost in loss record 14 of 15
==10844==    at 0x4C2677B: calloc (vg_replace_malloc.c:593)
==10844==    by 0x580F2FB: generic_gss_copy_oid_set (gssapi_alloc.h:43)
==10844==    by 0x58129D3: gss_acquire_cred (g_acquire_cred.c:195)
==10844==    by 0x518619D: dst_gssapi_acquirecred (gssapictx.c:306)
==10844==    by 0x155DC2: ns_tkeyctx_fromconfig (tkeyconf.c:114)
==10844==    by 0x14FA18: load_configuration (server.c:4963)
==10844==    by 0x150BB4: run_server (server.c:5381)
==10844==    by 0x60172F7: run (task.c:1012)
==10844==    by 0x6650850: start_thread (pthread_create.c:301)
==10844==    by 0x713A90C: clone (clone.S:115)
==10844== 
==10844== 94 (40 direct, 54 indirect) bytes in 1 blocks are definitely lost in loss record 15 of 15
==10844==    at 0x4C279EE: malloc (vg_replace_malloc.c:270)
==10844==    by 0x5817244: gss_import_name (g_imp_name.c:110)
==10844==    by 0x5186132: dst_gssapi_acquirecred (gssapictx.c:279)
==10844==    by 0x155DC2: ns_tkeyctx_fromconfig (tkeyconf.c:114)
==10844==    by 0x14FA18: load_configuration (server.c:4963)
==10844==    by 0x150BB4: run_server (server.c:5381)
==10844==    by 0x60172F7: run (task.c:1012)
==10844==    by 0x6650850: start_thread (pthread_create.c:301)
==10844==    by 0x713A90C: clone (clone.S:115)