xl: fix memory leaks in xl create

xl: fix memory leaks in xl create

Found using "valgrind xl create -n ..." and "valgrind xl create -e ..."

freeing config_data solves:
==18276== 944 bytes in 1 blocks are definitely lost in loss record 12 of 12
==18276==    at 0x4022F0A: malloc (vg_replace_malloc.c:236)
==18276==    by 0x404AEC1: libxl_read_file_contents (libxl_utils.c:258)
==18276==    by 0x8056865: create_domain (xl_cmdimpl.c:1314)
==18276==    by 0x8057E2D: main_create (xl_cmdimpl.c:3135)
==18276==    by 0x804B2FB: main (xl.c:76)
==18276==

Adding free_domain_config() solves the following (plus presumably others
which didn't trigger because I have no devices of that type).

d_config->disks:
==18276== 61 (32 direct, 29 indirect) bytes in 1 blocks are definitely lost in loss record 9 of 12
==18276==    at 0x4022F0A: malloc (vg_replace_malloc.c:236)
==18276==    by 0x4022F94: realloc (vg_replace_malloc.c:525)
==18276==    by 0x804E2D3: parse_config_data (xl_cmdimpl.c:715)
==18276==    by 0x8056A7C: create_domain (xl_cmdimpl.c:1347)
==18276==    by 0x8057E2D: main_create (xl_cmdimpl.c:3135)
==18276==    by 0x804B2FB: main (xl.c:76)

d_config->vifs:
==18276== 76 (48 direct, 28 indirect) bytes in 1 blocks are definitely lost in loss record 10 of 12
==18276==    at 0x4022F0A: malloc (vg_replace_malloc.c:236)
==18276==    by 0x4022F94: realloc (vg_replace_malloc.c:525)
==18276==    by 0x804E665: parse_config_data (xl_cmdimpl.c:779)
==18276==    by 0x8056A7C: create_domain (xl_cmdimpl.c:1347)
==18276==    by 0x8057E2D: main_create (xl_cmdimpl.c:3135)
==18276==    by 0x804B2FB: main (xl.c:76)

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>