core: rename Random* to RandomizedDelay*

The name RandomSec is too generic: "Sec" just specifies the default
unit type, and "Random" by itself is not enough. Rename to something
that should give the user general idea what the setting does without
looking at documentation.

man/systemd.timer.xml

@@ -205,7 +205,7 @@
       </varlistentry>
 
       <varlistentry>
-        <term><varname>RandomSec=</varname></term>
+        <term><varname>RandomizedDelaySec=</varname></term>
 
         <listitem><para>Delay the timer by a randomly selected, evenly
         distributed amount of time between 0 and the specified time
@@ -222,16 +222,16 @@
         time range in order to minimize wakeups, the former does the
         opposite: it stretches timer events over a time range, to make
         it unlikely that they fire simultaneously. If
-        <varname>RandomSec=</varname> and
+        <varname>RandomizedDelaySec=</varname> and
         <varname>AccuracySec=</varname> are used in conjunction, first
         the a randomized time is added, and the result is then
         possibly shifted further to coalesce it with other timer
         events possibly happening on the system. As mentioned above
         <varname>AccuracySec=</varname> defaults to 1min and
-        <varname>RandomSec=</varname> to 0, thus encouraging
+        <varname>RandomizedDelaySec=</varname> to 0, thus encouraging
         coalescing of timer events. In order to optimally stretch
         timer events over a certain range of time, make sure to set
-        <varname>RandomSec=</varname> to a higher value, and
+        <varname>RandomizedDelaySec=</varname> to a higher value, and
         <varname>AccuracySec=1us</varname>.</para></listitem>
       </varlistentry>