IMPALA-7628: skip test_tls_ecdh on Python 2.6
IMPALA-7628: skip test_tls_ecdh on Python 2.6

This is a temporary workaround. On the CentOS 6 build that failed
test_tls_v12, test_wildcard_san_ssl and test_wildcard_ssl were
all skipped so I figured this will unblock the tests without
losing coverage on most platforms that have recent Python.

Change-Id: I94ae9d254d5fd337774a24106eb9b08585ac0b01
Reviewed-on: http://gerrit.cloudera.org:8080/11519
Reviewed-by: Thomas Marshall <19143d3de8b13ab65aabdc921d14db5a16735b95@cmu.edu>
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala