2752/2755: Move test_cmdline code to test_arv-put.

Tim and I wrote tests for arv-put simultaneously.  This commit merges
them together.
2752: Rename test_arv_put.py.

This allows us to run specific test cases from the command-line.  The
hyphen in the filename prevented that before.
2752: arv-put works when it can't write a cache file.