Improve Jenkins docs build

Improve Jenkins docs build

- Use GMX_COMPACT_DOXYGEN=ON for per-patch set builds to save disk space
  and some running time.
- Build also the man and install-guide targets, which were previously
  missing.
- Make the build fail if it actually fails, and unstable if it just
  produces warnings.
- Make the end of the console output contain some useful information on
  what exactly failed.  This gets put into unsuccessful-reason.log,
  which can be used by Jenkins to show as the reason of the build
  failure when it reports back to Gerrit.
- Add options to the script to make it more convenient to test.

Fix some issues found in man page generation and in handling of
GMX_COMPACT_DOXYGEN.

Change-Id: Ice7622d7760c3dbd74f7b5b25700482d0a08e06b