standardize meta keys

[obbardc]

picax meta:

    <mediagen.media>cd</mediagen.media>
    <mediagen.media-label>MyLinux 0.1</mediagen.media-label>
    <mediagen.installer>debian-installer</mediagen.installer>
    <mediagen.arch>i386</mediagen.arch>
    <mediagen.inst-preseed-file>file:mypreseed</mediagen.inst-preseed-file>
    <mediagen.inst-base-url>file:64studio.com/boot/cdrom/</mediagen.inst-base-url>
    <mediagen.inst-cdrom-path>i386</mediagen.inst-cdrom-path>
    <mediagen.inst-udeb-include-list>pcmcia-cs-udeb</mediagen.inst-udeb-include-list>
    <mediagen.repository>hardy:main hardy:main/debian-installer</mediagen.repository>
    <mediagen.source>none</mediagen.source>
    <mediagen.no-order>True</mediagen.no-order>
    <mediagen.no-split>True</mediagen.no-split>

mediagen meta:

    <mediagen.media>img</mediagen.media>
    <mediagen.recipe>raspi</mediagen.recipe>
    <mediagen.debarch>armhf</mediagen.debarch>
    <mediagen.rootsize>1500</mediagen.rootsize>
    <mediagen.bootsize>64</mediagen.bootsize>
    <mediagen.outfile>out.img</mediagen.outfile>

    <mediagen.hostname>pideck</mediagen.hostname>
    <mediagen.root-password>toor</mediagen.root-password>
    <mediagen.preseed-conf>preseed.conf</mediagen.preseed-conf>
    <mediagen.postinst-script>postinst.sh</mediagen.postinst-script>

We should standardize the meta. Originally I didn't standardize it because there was issues with some of names, but this is no longer the case.