Add a simple testsuite for flux-core

This pull request adds a simple testsuite based on [sharness] to flux-core. The suite of tests
is composed of simple shell scripts which use helper functions to assert behavior of
commands. The main benefits of this approach is that it makes it extremely easy to add
new tests and run them.

For more detailed information, see the [README] in ./t of the pull request tree.

This pull request is currently *in progress*, still TODO:
 - The testsuite currently does not run with VPATH builds, and thus `make distcheck` is broken
 - Need verification that `$top_srcdir/t` is an ok place for the testsuite to live. This is
    just copied by convention from git
 - Not as important, but the test numbering scheme needs some thought. The main idea is
   that tests that build on other tests should be numbered such that they run last. Currently
   we just have `t0*.t` for foundational tests and `t1*.t` for kvs tests. Does this make sense.

To see examples of how these tests might be written, check out what is there already,
or the tests in [git] or [pdsh].  


[sharness]: https://mlafeldt.github.io/sharness/
[README]: https://github.com/grondo/flux-core/blob/testsuite-prototype/t/README.md
[git]: https://github.com/git/git/tree/master/t
[pdsh]: https://code.google.com/p/pdsh/source/browse/#git%2Ftests