Set cpuset cgroups for memlogd

[rouming]

PR sets cpuset cgroups for memlogd. The motivation of doing that is to move memlogd away from VM CPUs to avoid interference, so memlogd becomes being pinned to the CPU0 in default configuration.

Patches are:

1. dom0-ztools/010-eve-cgroup: a bit of refactoring

   Nothing special, just reduce copy-pastes.

2. dom0-ztools/002-logging,010-eve-cgroup: set cpuset cgroups for memlogd

   This patch does a few things:

   1. Moves memlogd to /eve/services cgroup folder since memlogd is a service anyway and this simplifies its cgroups settings.

   2. Sets cpuset.mems similar to cpuset.cpus. This gives possibility to add memlogd to cpuset tasks just in the 010-eve-cgroup. If cpuset.mems is not set an attempt to write pid to the 'tasks' cgroup file returns an error.

   3. Populates memlogd cpuset 'tasks' file with pids copied from 'memory' controller just to avoid games with listing threads of the memlogd process.

   The motivation of doing that is to move memlogd away from VM CPUs to avoid interference, so memlogd becomes being pinned to the CPU0 in default configuration.