event: Fix the error branch of riemann_event_create()

In riemann_event_create(), cache the result of riemann_event_set_va(),
and use that for the errno value in the error branch, instead of trying
to save errno, which the called function does not set.

Adjust the test case accordingly.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
tests: Use 127.0.0.1 instead of localhost

Switched the test suite to connect to 127.0.0.1 instead of localhost, as
the latter can resolve to ::1, while Riemann will - by default - listen
on 127.0.0.1 only.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
.travis.yml: Add coveralls support

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
README.md: Add Coveralls badge

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>