LU-11915 tests: use trusted.* xattr for conf-sanity test_115

LU-11915 tests: use trusted.* xattr for conf-sanity test_115

conf-sanity test 115 is always skipped because of patch
"LU-8569 linkea: linkEA size limitation". Links could not be
used for creating external inode for xattrs.

Let's use "trusted.*" xattrs for creating external xattr inode.

Fixes: 048a8740ae26 ("LU-8569 lfsck: handle linkEA overflow")

Signed-off-by: Artem Blagodarenko <c17828@cray.com>
Cray-bug-id: LUS-6966
Change-Id: If4c74c5baaeec6503edb3c5e756b9a55ff1bd90a
Test-Parameters: trivial testlist=conf-sanity envdefinitions=FLAKEY=false
Reviewed-on: https://review.whamcloud.com/34948
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>