packaging: verify sysctl.shmmax after modification

In non-developer mode, ovirt-engine-setup tries to modify
sysctl.shmmax.
This patch verifies that the above modification went correctly, and that
the current sysctl.shmmax is above what we need.

Change-Id: If2e1eafad9dacfa4d784526cdd0118c45cc47ccb
Signed-off-by: Ofer Schreiber <oschreib@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1033043