reduce inter-host delay for "justdoit"

30 minutes is a long tiem. It's important for "rotation" hosts, because
of timing issues described in:

199a62a1 delay hosts and shutdown should not be the same for rotation hosts

... but for "justdoit" hosts, it shouldn't matter.

howto/upgrades.md

@@ -177,11 +177,11 @@ currently can't unlock itself, naturally.
 This routine should be able to reboot all hosts with a `rebootPolicy`
 defined to `justdoit` or `rotation`:
 
-    echo "rebooting 'justdoit' hosts with a 10-minute delay, every 30 minutes...."
-    ./reboot -H $(ssh alberti.torproject.org 'ldapsearch -h db.torproject.org -x -ZZ -b ou=hosts,dc=torproject,dc=org -LLL "(rebootPolicy=justdoit)" hostname | awk "\$1 == \"hostname:\" {print \$2}" | sort -R') --delay-hosts=1800 --delay-shutdown=10 -v
+    echo "rebooting 'justdoit' hosts with a 10-minute delay, every 2 minutes...."
+    ./reboot -H $(ssh alberti.torproject.org 'ldapsearch -h db.torproject.org -x -ZZ -b ou=hosts,dc=torproject,dc=org -LLL "(rebootPolicy=justdoit)" hostname | awk "\$1 == \"hostname:\" {print \$2}" | sort -R') --delay-shutdown=10 -v
 
     echo "rebooting 'rotation' hosts with a 10-minute delay, every 30 minutes...."
-    ./reboot -H $(ssh alberti.torproject.org 'ldapsearch -h db.torproject.org -x -ZZ -b ou=hosts,dc=torproject,dc=org -LLL "(rebootPolicy=rotation)" hostname | awk "\$1 == \"hostname:\" {print \$2}" | sort -R') --delay-hosts=1800 --delay-shutdown=10 -v
+    ./reboot -H $(ssh alberti.torproject.org 'ldapsearch -h db.torproject.org -x -ZZ -b ou=hosts,dc=torproject,dc=org -LLL "(rebootPolicy=rotation)" hostname | awk "\$1 == \"hostname:\" {print \$2}" | sort -R') --delay-shutdown=10 --delay-hosts=1800 -v
 
 ### Rebooting KVM hosts