Server-to-server SSL connections with wildcard certs fails on Centos6.

After IMPALA-2905, test_wildcard_ssl started failing on CentOS 6 (but not Ubuntu). We already have one test xfailed because of CentOS 6 in that test suite. It looks like there is a separate incompatibility. We should build Impala on Centos 6 and determine if wildcard certs can work with the OpenSSL toolchain there. For now, the test is xfailed.