stbt.ocr: Handle more than one output file
stbt.ocr: Handle more than one output file

In a future commit I'm going to ask tesseract to write some debug
images, so we need to handle more than one file in the output directory.

While I'm here I'm dropping support for tesseract 3.02 which writes
".html" instead of ".hocr". There is no current LTS Ubuntu release with
a version of tesseract earlier than 3.03; Ubuntu 14.04 has 3.03. We
already dropped support for 3.02 elsewhere in commit 769ad0d
"stbt.ocr: Remove checks for ancient tesseract version".

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester