Improve test framework: tfw_quietly, tfw_multicolumn

New tfw_quieten() is similar to tfw_nolog(), but only silences the chatty log
output for asserts and other actions that succeed.  Failures are still logged.

New tfw_multicolumn() encapsulates an awk(1) script to format a list into
columns that fit into $COLUMNS width.

Improve exit status handling for test ERROR and FAIL conditions.
Improve Rhizome test defs: rhizome_list_dump

New rhizome_list_dump() reads a Rhizome list on standard input and formats the
output for easy reading in test logs, including only the columns named by its
arguments.

The assert_rhizome_list() function now sets the $rhizome_list_file_count global
variable.
Improve Rhizome Direct stress test

Reduce log verbosity, report extra files received by nodes, re-order
push/pull/sync process start order to increase chance of cross-fetching.
Add 'keyring' test script with three basic tests
Add keyring tests to 'all' test script