core: Try to initialize TERM from systemd.tty.term.console as well

We already have the systemd.tty.xxx kernel cmdline arguments for
configuring tty's for services, let's make sure the term cmdline
argument applies to pid1 as well.

man/kernel-command-line.xml

@@ -590,8 +590,10 @@
 
         <listitem><para>These arguments allow configuring default values for <varname>$TERM</varname>,
         <varname>TTYRows=</varname>, and <varname>TTYColumns=</varname> for tty
-        <replaceable>tty</replaceable>. The tty name should be specified without the
-        <filename>/dev/</filename> prefix (e.g. <literal>systemd.tty.rows.ttyS0=80</literal>).
+        <replaceable>tty</replaceable>. Additionally, <varname>systemd.tty.term.console</varname> will
+        configure the <varname>$TERM</varname> value used by <command>systemd</command> if not set explicitly
+        using <varname>TERM</varname> on the kernel command line. The tty name should be specified without
+        the <filename>/dev/</filename> prefix (e.g. <literal>systemd.tty.rows.ttyS0=80</literal>).
         </para></listitem>
       </varlistentry>
     </variablelist>

src/core/main.c

@@ -1425,6 +1425,12 @@ static int fixup_environment(void) {
         if (r < 0)
                 return r;
 
+        if (r == 0) {
+                r = proc_cmdline_get_key("systemd.tty.term.console", 0, &term);
+                if (r < 0)
+                        return r;
+        }
+
         t = term ?: default_term_for_tty("/dev/console");
 
         if (setenv("TERM", t, 1) < 0)