suite: fix build_matrix for + case

The + means we should concatenate everything in the directory.  Do that.

This was totally broken before (and unused until now).

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #217 from ceph/wip-fix-plus

suite: fix + handling
Give up on wait_until_healthy() after 15min

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>