CentOS sets a restrictive umask by default that will override the
rsyslog file permissions settings. This can cause our tempest tests
to no be able to read the log offload files in our CentOS gate jobs.
This patch clears this umask override in the devstack rsyslog
configuration.
Note: This is a global setting for rsyslog and you probably do not
want to set this outside of a testing environment.
Change-Id: I5962e335acff79152fa49c27c883aef2879593db
d56b9d65c1