Tagging release 004.051

[os] Small fix in base::os::debian to one of the systemd-related
syslog-filter regexes (akkornel)

[kerberos] Change the configuration for the WIN.SLAC.STANFORD.EDU domain,
as per Kent Reuber (see INC000003427399) (akkornel)

[rpm] Remove EL6 package requires of yum-plugin-downloadonly, since
yum-3.2.29-69 includes this plugin and obsoletes the individual
package (thus putting the puppet ensure in a loop) (jlent)
This tag has no release notes.