Suppress "hand-written" warnings during unittest

In certain cases, IssueRequester and DataStorer print warning messages.
For instance, if the server couldn't be contacted, the output directory
couldn't be found, etc.

This warnings are necessary and useful during production runs, however
they dirty the output from the unit tests.  This commit sets a
unit-test option called 'buffer', which buffers any stdout or stderr
output generated during the course of the tests, and prints it out if
the tests failed.