Convert manual shell tests to shelltestrunner

This is more of a RFC… Basically most of the shell-based tests are
converted from exec+grep to shelltestrunner.

Things are not all fine and nice though:

- we have dependencies between tests, as some generate some data files
  needed later; this is not nice, and we depend on serial execution in
  testrunner
- we can still fail with no so nice messages in the offline-test
  script (when we generate most of the data)

But overall, I think the tests are much nicer to
define/read/debug:

- each test is standalone, with the only dependency being an optional
  input data file; this is much better than a single monolithic shell
  script
- in case of failures, the failure is clearly shown by shell test,
  both for exit code and stdout/stderr
- shelltest can run in --debug mode, where the exact details are shown
  much better than the alternative of "set -x" for the shell script

Comments welcome!

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>