Add option to skip checking AppStream metadata

[abcfy2]

I meet this issue when use appimage plugin:

[appimage/stderr] 
[appimage/stderr] appimagetool, continuous build (commit 8bbf694), build <local dev build> built on 2020-12-31 11:48:33 UTC
[appimage/stderr] Using architecture x86_64
[appimage/stderr] AppStream upstream metadata found in usr/share/metainfo/org.qbittorrent.qBittorrent.appdata.xml
[appimage/stdout] org.qbittorrent.qBittorrent.appdata.xml
[appimage/stdout]   E: org.qbittorrent.qBittorrent:19: description-para-markup-invalid ul
[appimage/stdout]   E: org.qbittorrent.qBittorrent:27: description-para-markup-invalid ul
[appimage/stdout]   E: org.qbittorrent.qBittorrent:39: description-para-markup-invalid ul
[appimage/stdout]   I: org.qbittorrent.qBittorrent:71: url-not-secure http://bugs.qbittorrent.org/
[appimage/stdout]   I: org.qbittorrent.qBittorrent:73: url-not-secure http://forum.qbittorrent.org/
[appimage/stdout]   W: org.qbittorrent.qBittorrent:73: url-not-found http://forum.qbittorrent.org/ - HTTP 503: Service Unavailable
[appimage/stdout] 
[appimage/stdout] 验证失败：错误：3, 警告：1, 信息：2, pedantic: 4
[appimage/stdout] run_external: subprocess exited with status 3[appimage/stderr] Failed to validate AppStream information with appstreamcli
ERROR: Failed to run plugin: appimage (exit code: 1) 

Thanks.

[TheAssassin]

Please file this issue over at https://github.com/AppImage/AppImageKit/.

[abcfy2]

Thanks @TheAssassin . I've check upstream issue: AppImage/AppImageKit#313

It said can use the -n, --no-appstream: Do not check AppStream metadata option of appimagetool. But how can I set this option to plugin appimage?

[TheAssassin]

I suppose we need to expose that argument in some way. I'll reopen this issue, but will change the title.

[TheAssassin]

Fixed in latest build.