fix: cluster/local-override.conf does not take effect at vm.args/app.config

[zhongwencool]

Config changes such as log levels etc can be applied from dashboard in realtime. However due to the sys.config (or app.config) generation did not take cluster-override (nor local-override) into account. such config change are not persisted.

This PR tries to include both cluster and local overrides into config generation stage.

• [x] Verify space is allowed in data_dir config (and env override)
• [ ] Fix emqx.cmd for Windows

[coveralls]

Pull Request Test Coverage Report for Build 3049662246

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 33 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.03%) to 77.361%

---

Files with Coverage Reduction	New Missed Lines	%
apps/emqx_conf/src/emqx_conf_schema.erl	1	92.31%
apps/emqx_dashboard/src/emqx_dashboard_monitor.erl	1	69.44%
apps/emqx/src/emqx_broker.erl	1	81.87%
apps/emqx/src/emqx_cm.erl	1	88.99%
apps/emqx/src/emqx_limiter/src/emqx_limiter_schema.erl	1	85.92%
apps/emqx/src/emqx_logger_textfmt.erl	1	47.37%
apps/emqx/src/emqx_message.erl	1	94.12%
apps/emqx/src/emqx_router_utils.erl	1	60.47%
apps/emqx_gateway/src/mqttsn/emqx_sn_frame.erl	2	64.04%
apps/emqx/src/persistent_session/emqx_persistent_session.erl	2	93.01%
<!--	Total:	33

Totals
Change from base Build 3049512272:	-0.03%
Covered Lines:	20626
Relevant Lines:	26662

---

💛 - Coveralls

[zhongwencool]

fix emqx.cmd for windows too. also: test space in data dir.

/data1/test good/ is ok.

I'm not familiar with cmd on windows, I don't have a windows environment to debug, maybe find someone to help this out.

[zmstone]

will fix windows in another PR.

[zmstone]

as discussed. we will need to fix it in a different approach. the hocon_cli is not quite helpful in this case. we'll need to perform config generation just like how emqx_config:init_load does:

1. load base config (emqx.conf + merge envs)
2. read data_dir from loaded base config, so we know where the {cluster|loca}-override.conf files are, and also know to generate the app.<time>.config file.
3. applycluster-overrides.conf + local-overrides.conf on top of the base config
4. generate app..config