reserve workflow: tell the user if their recipe matches no systems

Bug: 1062086
Change-Id: I2c1876fb81e4163009b6423bbda8863fa55cac10
fix cloning of reserve workflow jobs with a LC requirement

The bug was just that the XML being stored in recipe.host_requires did
not have an enclosing <hostRequires/> element, which is expected by the
cloning process.

Bug: 1144205
Change-Id: Ieb824970857850e959d599b410e6427c74ece024