Use built-in DRBD module instead of building it manually in setup_nfs_ha.sh

[hosungsmsft]

Starting from the ubuntu-azure kernel version 4.15.0-1018-azure, the DRBD kernel module is now built in the default kernel modules package (linux-modules-4.15.0-1018-azure) thanks to Azure LIS team's effort, so we should stop building our own custom kernel module in setup_nfs_ha.sh, but just use the built-in module. Note that the built-in module's DRBD version is 8.9, whereas the custom build is with version 9.0. The drbd-utils package from the Ubuntu repo will be also about version 8.x, and there seem to be some incompatibility between the two version on the drbdadm command (e.g., no drbdadm status available with the drbd-utils package version), so related commands should be changed accordingly as well.