config-host.mak: rename confdir to qemu_confdir

$confdir is a confusing name, as it's not clear if it's "the system
config dir" or "the Qemus-specific directory inside the config dir".
$qemu_confdir makes it more clear.

The current C code that uses CONFIG_QEMU_CONFDIR should be safe, as now
create_config generates the same #define name (CONFIG_QEMU_CONFDIR) for
both "confdir" and "qemu_confdir" variables.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -3025,7 +3025,7 @@ echo "mandir=$mandir" >> $config_host_mak
 echo "qemu_datadir=$qemu_datadir" >> $config_host_mak
 echo "sysconfdir=$sysconfdir" >> $config_host_mak
 echo "docdir=$qemu_docdir" >> $config_host_mak
-echo "confdir=$qemu_confdir" >> $config_host_mak
+echo "qemu_confdir=$qemu_confdir" >> $config_host_mak
 echo "libexecdir=\${prefix}/libexec" >> $config_host_mak
 echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"" >> $config_host_mak
 echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"" >> $config_host_mak