Revert "core.lua: Improve setup of cgroups hierarchies, should fix issue #45"

I came to conclusion that supporting multiple cgroups subsystems mounted in
single hierarchy is a bad thing.

This reverts commit ad5474c89ff2a8738abd013f51f3aeacd748f79f.
split src/core.lua to modules inside src/lua/

I want to split core.lua because it is too long.
core.lua is split into:

- src/lua/bootstrap.lua (called from C; loads everything else)
- src/lua/misc.lua (functions which don't fit elsewhere)

- src/lua/string.lua
- src/lua/table.lua

- src/lua/ulatency.lua
- src/lua/u_proc.lua
- src/lua/cgroup.lua
Add function ulatency.log_message(msg)
Fix error logging when task cannot be moved to cgroup
Improve error handling while mounting cgroups subsystems

Test for various error conditions while mounting cgroup hierarchies
(both with subsystem controller attached and hierarchies
private to ulatencyd)

Fail on any of following conditions:

- Multiple subsystems mounted in single hierarchy.
- Subsystem already mounted in other than standard location
  CGROUP_ROOT/<subsys> or CGROUP_ROOT_PRIVATE/<subsys>
  for private hierarchies (further referenced just by "mount point").
- Required mount point exists but is not a directory.
- Something else already mounted in mount point.
- Some available and enabled subsystem could not be mounted.

- Log verbose errors if something fails.
Log fatal errors to stderr.

So user is briefly informed what failed if ulatencyd is being run
from tty.
ulatency --cmd: fix if /proc/#/cmdline contains UTF-8 chars
in bootstrap.lua set parameters for root cgroup of each subsystem

This allows new cgroups inherit essential parameters from the root
cgroup. Like memory.move_charge_at_immigrate in memory cgroup or
cgroup.clone_children in in cpuset cgroup.

This must be done before scheduler is run, because filters may create
cgroups too. Currently Isolate filter does so.


cgroups.conf: add CGROUP_ROOT_DEFAULT table definition.
CGroup.new() sets cgroup parameters accoding to CGROUP_DEFAULT or
CGROUP_ROOT_DEFAULT
Fix SMP: Attach isolated cpuset cgroups to all online CPUs
Fix counting of scheduler iterations