Combine all 3 shellouts into one script, retrieveMetaData.sh.
The script is executed by /bin/sh by default, it can be changed for
Windows users by setting $wgPdfHandlerShell.
pdftotext is a bit special since it's behavior varies based on the
program's exit code, so save that in a file so we can check it
independently of the overall exit status.
Bug: T289228
Change-Id: I29750bcc282bd5f9b8e2f79aa340869738ea5f5b
