When restarting services, don't attempt to restart a service if it is disabled/masked or the `systemctl restart` command will fail, causing the calling command (e.g., `config load`, `config reload`, `config load_minigraph`) to error out.

- Ensure all features (services) are in the configured state when hostcfgd starts
- Better functionalization of code
- Also replace calls to deprecated `has_key()` method in `tacacs_server_handler()` and `tacacs_global_handler()` with `in` keyword.

This PR depends on sonic-net/sonic-utilities#944, otherwise `config load_minigraph` will fail when trying to restart disabled services.

When building the SONiC image, used systemd to mask all services which are set to "disabled" in init_cfg.json.

This PR depends on sonic-net/sonic-utilities#944, otherwise `config load_minigraph will fail when trying to restart disabled services.

- Ensure all features (services) are in the configured state when hostcfgd starts
- Better functionalization of code
- Also replace calls to deprecated `has_key()` method in `tacacs_server_handler()` and `tacacs_global_handler()` with `in` keyword.

This PR depends on sonic-net/sonic-utilities#944, otherwise `config load_minigraph` will fail when trying to restart disabled services.

When building the SONiC image, used systemd to mask all services which are set to "disabled" in init_cfg.json.

This PR depends on sonic-net/sonic-utilities#944, otherwise `config load_minigraph will fail when trying to restart disabled services.

When restarting services, don't attempt to restart a service if it is disabled/masked or the `systemctl restart` command will fail, causing the calling command (e.g., `config load`, `config reload`, `config load_minigraph`) to error out.

 [201911][thermal control] Backport changes from master branch (sonic-net#929)
     [201911][config] Support abbreviation (sonic-net#933)
       Add 'hw-management-generate-dump.sh' to 'show techsupport'
       command (sonic-net#934)
       [fwutil]: Update fwutil to v2.0.0.0. (sonic-net#942)
       Fixes bug for PFCWD feature parameters (sonic-net#838)
     Fixed fast-reboot for BFN platform (sonic-net#871)
     [config] Add 'interface transceiver' subgroup with 'lpmode' and
     'reset' subcommands (sonic-net#904)
      [warm-reboot]: added pre-check for ISSU file (sonic-net#915)
       [config] Don't attempt to restart disabled services (sonic-net#944)