xfstests: Introduce a results directory

xfstests: Introduce a results directory

Currently each test gets it's sequence number from it's name. It
separates this from the path via basename, and uses it for
outputting full, notrun and other status/log files. Hence these end
up in the top level directory.

All these output files need to go somewhere other than the top level
directory. Right now the check script is looking for them in the new
test directories (e.g. for the notrun files), but it would be good
to be able to separate the test source form the test output.

Hence create an output directory which has a similar heirarchy to
the test source directory. Create it on demand when we build the
list of tests to run if it doesn't already exist.

Change the high level check script to set up this variable
appropriately for each test that is being run, and to use this new
output directory for it's result files as well. The next commit will
change all the tests themselves to use the new output directory.

This is the first (small) step in being able to store test results
in an external location for archival/data mining purposes.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Phil White <pwhite@sgi.com>
[rjohnston@sgi.com rm whitespace and fix typos in commit message]
Signed-off-by: Rich Johnston <rjohnston@sgi.com>