add cpuacct_cgroup collector

This measure utime and stime of system as well as cgroups with 'gauge' type
Merge pull request #244 from action-io/cpuacct

Measure cpu's total user and system time of system and cgroups
pep8
Bugfix: new handlers not detected on reload.
Merge pull request #245 from Supy/handler-reload-bugfix

Bugfix: new handlers not detected on reload.
Set CpuAcctCgroupCollector disabled by default
Merge remote-tracking branch 'upstream/master'