util: don't use virFirewallRuleToString() to log the rule being applied

util: don't use virFirewallRuleToString() to log the rule being applied

Instead of separately building the commandline into a string to log,
just wait a few lines until we've built the virCommand object, and
call virCommandToString, which does the same thing.

(As a bonus, we were already calling virCommandToString to put the
commandline in a string in case of a failure when running it - from
the point of view of *that* usage, we're just moving the call to
virCommandToString *up* a few lines, i.e. we now only construct the
commandline string once.)

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>