tests: save 9 characters for asok paths

tests: save 9 characters for asok paths

For vstart.sh powered tests, save 9 characters in the path name
by replacing testdir/test- with td/t-

60 characters imposed by jenkins
9 characters for src/test
5 characters for td/t-

33 left (instead of 24) for the test to create asok such as out/client.admin.25327.asok

Moving these files outside of the build directory is a bad idea because
tests should only create/use files within the builddir and not write
outside of this directory. Doing so would make things more complicated
for cleanup in case the test fail and create other problems as a
consequence (filling out disk space, conflicting directories between
runs etc.).

For ceph-helpers.sh tests replace testdir with td, saving 5 characters.
This is not strictly necessary but keeps the directory names consistent:
if the developer wants to get rid of all the test leftovers, it is
enough to remove the a single directory: td.

Fixes: http://tracker.ceph.com/issues/16014
Signed-off-by: Loic Dachary <loic@dachary.org>