ASM-2659 Add backend support for NTP for Red Hat deployments

Updated the kickstart and post_install ERB files to include the timezone and NTP configuration during the initial installation.
This will take care of the case where servers are reported to have time lag between resulting in the failure of puppet agent not check-in with puppet master
Updated as per the code comments

Instead of getting the data from the new ntp_config ERB file, get the information from install_options hash created by asm::server
NTP configuration for vmware_esxi to take care of puppet agent time-lag
Updated command set for RHEL 7 for enabling and starting the NTP service
Merge pull request #43 from sushilrai/rhel_ntp

ASM-2659 Add backend support for NTP for Red Hat deployments