Tests failing on memcache backend (memcache testing disabled in trunk)

While migrating tests to the new multi-conf testing approach, I discovered that memcache tests were failing (since we hadn't been running them for CI). The memcache configuration template is currently commented out from run_tests.py, as it's failing to create the first token in bin/sampledata.sh

To enable testing against the memcache backend, uncomment 'memcache.conf.template' from keystone/test/run_tests.py:

    CONFIG_FILES = (
        'sql.conf.template',
        #'memcache.conf.template',
        'ldap.conf.template')