fix(install.sh): skip checking for sse4 2 flag if kvm was detected (#485)

This PR disables checking for the SSE4.2 flag, which may not be present if the server is running in a VM even if SSE4.2 is in fact available to use (ClickHouse/ClickHouse#20). The KVM check was obtained from a comment in that issue.

If SSE4.2 is not actually available in the VM, then the installation script may fail in an unpredictable way. Perhaps we can add a keyword argument to the script to let the user decide if they want to skip the check.