log verbosity at runtime; log modules; remove glog; unify (major update)

* New: set log verbosity at runtime: entire cluster or selected node(s);
  entire software or specific (log) modules.
=======================================================================
* deprecate glog-provided (flag-based) verbosity, severity, vmodules, etc.
* remove much of the glog code (finally)
* consistently use configured persistent log settings across the board
* add user-friendly `ais config` CLI
* add log modules: `mirror`, `ETL`, `dsort`, `downloader`
* consolidate log modules in one place
  - remove the latter from debug_on and glog sources
* deprecate and remove `AIS_DEBUG`
* update docs/development.md and docs/getting_started.md
* separately, optimize glog locking - reduce the scope
* aisnode: add flag set (and discard imported modules' flags)

Signed-off-by: Alex Aizman <[email protected]>

.golangci.yml

@@ -111,18 +111,6 @@ linters-settings:
     disable:
       - fieldalignment # TODO: Enable, for now reports a lot of problems.
       - shadow # Reports a lot of false-positives and conflicts with other linters.
-    settings:
-      printf: # Analyzer name, run `go tool vet help` to see all analyzers.
-        funcs: # Run `go tool vet help printf` to see available settings for `printf` analyzer.
-          - github.com/NVIDIA/aistore/3rdparty/glog.Infof
-          - github.com/NVIDIA/aistore/3rdparty/glog.Warningf
-          - github.com/NVIDIA/aistore/3rdparty/glog.Errorf
-          - github.com/NVIDIA/aistore/3rdparty/glog.Fatalf
-          - github.com/NVIDIA/aistore/cmn/debug.Assertf
-          - github.com/NVIDIA/aistore/cmn/debug.Errorf
-          - github.com/NVIDIA/aistore/cmn/debug.Infof
-          - github.com/NVIDIA/aistore/cmn/cos.Exitf
-          - github.com/NVIDIA/aistore/cmn/cos.ExitLogf
   golint:
     min-confidence: 0
   errcheck: