xfstests: fix last test runtime output

xfstests: fix last test runtime output

Prior to the test directory split-up, xfstests used to output the
time it previously took to run a specific test in it's output. This
was broken during the split up, as test identifiers changed and the
result output changed.

To fix this, the search for previous test results needs to look at
the sequence number rather than the absolute sequence for the test.
The new output looks the same as the old functionality:

generic/001 4s ... 5s
generic/002 1s ... 0s
generic/005 1s ... 1s
generic/006 1s ... 1s
generic/007 2s ... 1s

Where the first column is the time of the previous test run, and the
second column is the time that this run took.

Further, the check files used to generate this information are not
being output properly in the result directory, and so various log
files are not getting written to the correct location or file names.
For example, the calls to _check_test_fs would output failures to
".full", while other messages would be output to check.full, but
none would output to the corect location of RESULT_BASE/check.full.

Fix all this mess up so that all the check files for a specific run
end up in RESULT_BASE, and ensure the timing code checks the right
file and dumps output.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>