appmonitor test: avoid /usr/share
appmonitor test: avoid /usr/share

Set XDG_DATA_DIRS to make sure we don't use /usr/share from the
appmonitor test.  We will soon throw a warning if we find defaults.list,
so make sure we don't open ourselves up to that if there is one on the
system.

https://bugzilla.gnome.org/show_bug.cgi?id=728040

cention-sany/glib,lukasz-skalski/glib,MathieuDuponchelle/glib,Distrotech/glib,ieei/glib,cention-sany/glib,MathieuDuponchelle/glib,tchakabam/glib,endlessm/glib,krichter722/glib,cention-sany/glib,cention-sany/glib,tchakabam/glib,johne53/MB3Glib,tchakabam/glib,mzabaluev/glib,lukasz-skalski/glib,lukasz-skalski/glib,ieei/glib,endlessm/glib,endlessm/glib,ieei/glib,johne53/MB3Glib,Distrotech/glib,endlessm/glib,gale320/glib,ieei/glib,MathieuDuponchelle/glib,tchakabam/glib,lukasz-skalski/glib,endlessm/glib,krichter722/glib,Distrotech/glib,tamaskenez/glib,mzabaluev/glib,johne53/MB3Glib,cention-sany/glib,johne53/MB3Glib,mzabaluev/glib,gale320/glib,ieei/glib,lukasz-skalski/glib,MathieuDuponchelle/glib,gale320/glib,MathieuDuponchelle/glib,tamaskenez/glib,gale320/glib,johne53/MB3Glib,tamaskenez/glib,mzabaluev/glib,tamaskenez/glib,gale320/glib,krichter722/glib,tchakabam/glib,Distrotech/glib,Distrotech/glib,johne53/MB3Glib,krichter722/glib,tamaskenez/glib,mzabaluev/glib,krichter722/glib