[job_resource_manager] deactivate memory cgroup

If you want to use the memory cgroup features then:

 1. Check that your kernel supports it (cat /proc/cgroups).
    Under Debian you have to add "cgroup_enable=memory" to the kernel
    append

 2. Edit /etc/oar/job_resource_manager_cgroups.pl and change the line to:

        my $ENABLE_MEMCG = "YES";
[job_resource_manager] /bin/dash compatibility

On Debian, Perl "system" statement calls /bin/sh as the interpreter so
/bin/dash.
[oarsh_shell] fix job env file issue

Now the oar.conf is sourced inside oarsh_shell. So the variable
OAR_RUNTIME_DIRECTORY is up to date.
[doc] fix syntax
[oar_resource_add] bugfix core and threads options