"Essentially they did. It was an expression of strained optimism, not propaganda."
Not entirely - the idea of 'a short war did appear on official documents such as the one on agriculture, cited above, and it became part of Horatio Bottomley's 'easie-peasie pantomime' shows, as shown in the first Paxman programme.
If it was wishful thinking, it was not discouraged by the recruiters.
From a Wiki entry on the economics of the war
"All of the powers in 1914 expected a short war; none had made any economic preparations for a long war, such as stockpiling food or critical raw materials. The longer the war went on, the more the advantages went to the Allies, with their larger, deeper, more versatile economies and better access to global supplies. As Broadberry and Harrison conclude, once stalemate set in late in 1914:"   
Wiki again:
"Over by Christmas
When the war began both sides believed, and publicly stated, that the war would end soon."
Ambivalence rules OK, it would appear
Jim Carroll