tree-wide: Replace archive-z2 with archive

In almost all places. There are just a few exceptions; one tricky bit for
example is that the repo config must still have `mode=archive-z2`, since
`archive` used to mean something else. (We could very likely just get rid of
that check, but eh, later).

I also added a test that one can still do `ostree repo init --mode=archive-z2`.

Closes: #1125
Approved by: jlebon

man/ostree-init.xml

@@ -67,9 +67,13 @@ Boston, MA 02111-1307, USA.
         <variablelist>
             <varlistentry>
                 <term><option>--mode</option>="MODE"</term>
-                <listitem><para>
-                    Initialize repository in given mode (bare, bare-user, archive-z2).  Default is "bare".
-                </para></listitem>
+                <listitem><para> Initialize repository in given mode
+                (<literal>bare</literal>, <literal>bare-user</literal>,
+                <literal>archive</literal>). The default is
+                <literal>bare</literal>. Note that for
+                <literal>archive</literal> the repository configuration file
+                will actually have <literal>archive-z2</literal>, as that's the
+                historical name.</para></listitem>
             </varlistentry>
 
             <varlistentry>

man/ostree-pull.xml

@@ -157,7 +157,7 @@ Boston, MA 02111-1307, USA.
 
 	<para>Perform a complete mirror of the remote.  (This is
 	likely most useful if your repository is also
-	<literal>archive-z2</literal> mode)</para>
+	<literal>archive</literal> mode)</para>
 
         <para><command>$ ostree --repo=repo pull remote_name exampleos/x86_64/standard</command></para>
 

man/ostree.repo-config.xml

@@ -76,7 +76,7 @@ Boston, MA 02111-1307, USA.
     <variablelist>
       <varlistentry>
         <term><varname>mode</varname></term>
-        <listitem><para>One of <literal>bare</literal>, <literal>bare-user</literal> or <literal>archive-z2</literal>.  </para></listitem>
+        <listitem><para>One of <literal>bare</literal>, <literal>bare-user</literal> or <literal>archive-z2</literal> (note that <literal>archive</literal> is used everywhere else.)</para></listitem>
       </varlistentry>
 
       <varlistentry>