I haven't used the OpenGeoSuiteSDK lately but I guess you could just use the GetMap-URL which will probably look like this: http://localhost/cgi-bin/qgis_mapserv.fcgi?map=/home/hast/UA/qgis-mapnik.qgs

Have you tried the following yet?:

    qgis: {
            ptype: "gxp_wmssource",
            url: "http://localhost/cgi-bin/qgis_mapserv.fcgi?map=/home/hast/UA/qgis-mapnik.qgs",
            version:"1.1.1"
        },  
    
//////////
    	
        {
            source: "qgis",
            title: "QGIS Server Layer",
            name: "buildings",
            opacity: 1
         } 

Edit1: Just gave it a try and it works for me ;)

I also added a proxy config, as my QGIS-Server deliveres the tiles on a different port:

    var app = new gxp.Viewer({
        proxy: "proxy/?url=",

...........

and added the override for ExtJS

     * @require overrides/override-ext-ajax.js

![enter image description here][1]


  [1]: https://i.sstatic.net/mxetT.jpg