core: Move cpu_over_commit from VdsDynamic to VdsStatistics

cpu_over_commit field is rapidly changing, and should be located in VdsStatistics.
This patch moves it to vds_statistics and updates the relevant stored procedures
and DAOs

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1114285
Change-Id: I4cf1d83f67385e4259f8f554ff3b81c68b751122
Signed-off-by: lzelkha@redhat.com <lzelkha@redhat.com>