selftest/flapping: mark samba4.nss.test using winbind as flakey

selftest/flapping: mark samba4.nss.test using winbind as flakey

[1427/1518 in 1h12m39s] samba4.nss.test using winbind(member)
UNEXPECTED(failure): samba4.nss.test using winbind(member).run nsstest(member)
REASON: _StringException: _StringException: ERROR setpwent: NSS_STATUS=-1  1 (nss_errno=0)
ERROR getpwent: NSS_STATUS=-1  1 (nss_errno=0)
ERROR endpwent: NSS_STATUS=-1  1 (nss_errno=0)
ERROR setgrent: NSS_STATUS=-1  1 (nss_errno=0)
ERROR getgrent: NSS_STATUS=-1  1 (nss_errno=0)
ERROR endgrent: NSS_STATUS=-1  1 (nss_errno=0)
ERROR Non existent user gave error -1
ERROR Non existent uid gave error -1
ERROR Non existent group gave error -1
ERROR Non existent gid gave error -1
total_errors=10

This seems to happen in all environments

metze