Switch from mkpasswd to uuidgen in rpm spec file

uuidgen lives in e2fsprogs which is almost always installed, unlike
mkpasswd which lives in expect, so change to using uuidgen.  No change
for installed systems.

redhat/varnish.spec

@@ -17,7 +17,7 @@ Requires: logrotate
 Requires: ncurses
 Requires: pcre
 Requires(pre): shadow-utils
-Requires(post): /sbin/chkconfig, /usr/bin/mkpasswd
+Requires(post): /sbin/chkconfig, /usr/bin/uuidgen
 Requires(preun): /sbin/chkconfig
 Requires(preun): /sbin/service
 Requires(preun): initscripts
@@ -218,7 +218,7 @@ exit 0
 /sbin/chkconfig --add varnish
 /sbin/chkconfig --add varnishlog
 /sbin/chkconfig --add varnishncsa 
-test -f /etc/varnish/secret || (mkpasswd > /etc/varnish/secret && chmod 0600 /etc/varnish/secret)
+test -f /etc/varnish/secret || (uuidgen > /etc/varnish/secret && chmod 0600 /etc/varnish/secret)
 
 %preun
 if [ $1 -lt 1 ]; then