integration tests: Improve message when ZNC is missing
integration tests: Improve message when ZNC is missing

Previously, "more or less unrelated" things would fail. After this
change, also a message is printing that gives a hint on what went wrong.

Signed-off-by: Uli Schlachter <346c0ad49ac8427b61b3b55abbe37dc0ebd524f2@znc.in>

elyscape/znc,Zarthus/znc,Zarthus/znc,znc/znc,elyscape/znc,markusj/znc,GLolol/znc,Phansa/znc,znc/znc,dgw/znc,evilnet/znc,jreese/znc,jreese/znc,evilnet/znc,znc/znc,psychon/znc,markusj/znc,psychon/znc,GLolol/znc,elyscape/znc,Phansa/znc,Phansa/znc,jreese/znc,GLolol/znc,kashike/znc,psychon/znc,BtbN/znc,Zarthus/znc,Phansa/znc,BtbN/znc,DarthGandalf/znc,jreese/znc,evilnet/znc,znc/znc,Phansa/znc,psychon/znc,evilnet/znc,Zarthus/znc,dgw/znc,evilnet/znc,BtbN/znc,kashike/znc,jreese/znc,DarthGandalf/znc,kashike/znc,dgw/znc,GLolol/znc,DarthGandalf/znc,psychon/znc,znc/znc,markusj/znc,markusj/znc,jreese/znc,BtbN/znc,GLolol/znc,GLolol/znc,markusj/znc,Phansa/znc,DarthGandalf/znc,kashike/znc,DarthGandalf/znc,dgw/znc,dgw/znc,kashike/znc,evilnet/znc,BtbN/znc,elyscape/znc,BtbN/znc,znc/znc,Zarthus/znc,DarthGandalf/znc,elyscape/znc,kashike/znc,dgw/znc,elyscape/znc,markusj/znc,psychon/znc,Zarthus/znc