LU-1943 tests: unlink all files when mdsrate times out

LU-1943 tests: unlink all files when mdsrate times out

Port of ORI-453 to the master

When mdsrate cannot create the requested number of files in the
allocated timeframe (i.e. the --time option), filenames are not
necessarily consecutive and can have an index higher than the
number of files that was actually created. Here is an example:

0: iters 0 nfiles 100000 time 1 begin 0 end 99998 dirthreads 2.
1: iters 0 nfiles 100000 time 1 begin 1 end 99999 dirthreads 2.
0: client-4.lab.whamcloud.com starting at Mon Jan  9 08:26:07 2012
1: client-12.lab.whamcloud.com starting at Mon Jan  9 08:26:07 2012
0: created 1884 files, last file 'f3766'.
Rate: 2470.42 eff 2470.59 aggr 1235.29 avg client creates/sec
     (total: 2 threads 2440 creates 1 dirs 2 threads/dir 0.99 secs)
0: client-4.lab.whamcloud.com finished at Mon Jan  9 08:26:08 2012
1: created 556 files, last file 'f1111'.
1: client-12.lab.whamcloud.com finished at Mon Jan  9 08:26:08 2012

2440 files have been created and the last file name was f1111 for
rank 1 and f3766 for rank 0. Running mdsrate --unlink --nfiles 2440
in this case would discard all files with an index >= 2440.

With this patch, each mdsrate task will complete properly and report
the right number of executed operation as soon as one file is missing
in the per-task sequence. This behavior can be changed with the
--ignore and --recreate option which are already available.
This way, mdsrate --unlink --nfiles 100000 will work fine in the
example above since it will unlink all the existing files, without
doing tons of useless lookups.

Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Signed-off-by: Mikhail Pershin <tappro@whamcloud.com>
Change-Id: I96f690ad0f36c65353bbc5a401455479b4c3783b
Reviewed-on: http://review.whamcloud.com/4195
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>