Don't remove the /var/run/jail_name.id file if a jail fails to start.

This messes up ezjail (and possibly others), when attempting to start
a jail that already exists.

PR:		208806
Reviewed by:	tj
MFC after:	5 days

etc/rc.d/jail

@@ -489,7 +489,6 @@ jail_start()
 			if _jid=$($jail_jls -j $_j jid); then
 				echo "$_jid" > /var/run/jail_${_j}.id
 			else
-				rm -f /var/run/jail_${_j}.id
 				echo " cannot start jail " \
 				    "\"${_hostname:-${_j}}\": "
 			fi
@@ -513,7 +512,6 @@ jail_start()
 				_jid=$($jail_jls -j $_j jid)
 				echo $_jid > /var/run/jail_${_j}.id
 			else
-				rm -f /var/run/jail_${_j}.id
 				echo " cannot start jail " \
 				    "\"${_hostname:-${_j}}\": "
 				cat $_tmp