The “ensure-dirs” script as included in Ganeti 2.3 is very slow when
working with big queues requiring a change of permissions on many or all
files.

$ find /var/lib/ganeti/queue/ | wc -l
52354

Before this change:
$ time /usr/local/lib/ganeti/ensure-dirs -f
real    16m4.739s

While not adressed in this patch, I'd like to record the overall
ineffiency of the “ensure-dirs” script, even after this change:

$ time /usr/local/lib/ganeti/ensure-dirs -f
real    5m57.362s
[…]
$ strace -e clone,execve -f -c /usr/local/lib/ganeti/ensure-dirs -f
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 50.08    5.147090          49    104774           clone
 49.92    5.131094          49    104739           execve

More changes will be needed. Just for comparision, a small Python
snippet changing permissions on all files (“ensure-dirs” changes the
owner too):

$ time python -c 'import os; from ganeti import utils;
[os.chmod(i, 0644) for i in
utils.ListVisibleFiles("/var/lib/ganeti/queue/archive/big")]'
real    0m0.605s
[…]

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>