cephadm: add --dry-run option to cephadm {enter,logs,unit} commands

Add a --dry-run option to the cephadm enter, cephadm logs, and
cephadm unit commands. Like cephadm shell --dry-run, this causes cephadm
to print the command it would have run rather than running said command.
This allows the user to copy and edit or otherwise hack on the output
to make variations on these comands without having to teach cephadm all
the possible options and switches those commands make take.
For instance I can follow recent mgr logging like so:
```
$(/tmp/cephadm logs -i mgr --dry-run | sed 's/ / --since=-1s -f /')
```

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

src/cephadm/cephadm.py

@@ -3171,6 +3171,9 @@ def command_enter(ctx: CephadmContext) -> int:
         container_args=container_args,
     )
     command = c.exec_cmd(command)
+    if ctx.dry_run:
+        print(' '.join(shlex.quote(arg) for arg in command))
+        return 0
     return call_timeout(ctx, command, ctx.timeout)
 
 ##################################
@@ -3238,9 +3241,13 @@ def command_unit(ctx: CephadmContext) -> int:
     unit_name = lookup_unit_name_by_daemon_name(
         ctx, ident.fsid, ident.daemon_name
     )
+    command = ['systemctl', ctx.command, unit_name]
+    if ctx.dry_run:
+        print(' '.join(shlex.quote(arg) for arg in command))
+        return 0
     _, _, code = call(
         ctx,
-        ['systemctl', ctx.command, unit_name],
+        command,
         verbosity=CallVerbosity.VERBOSE,
         desc='',
     )
@@ -3260,6 +3267,9 @@ def command_logs(ctx: CephadmContext) -> None:
     if ctx.command:
         cmd.extend(ctx.command)
 
+    if ctx.dry_run:
+        print(' '.join(shlex.quote(arg) for arg in cmd))
+        return
     # call this directly, without our wrapper, so that we get an unmolested
     # stdout with logger prefixing.
     logger.debug('Running command: %s' % ' '.join(cmd))
@@ -4770,6 +4780,10 @@ def _get_parser():
         '--fsid',
         help='cluster FSID')
     _name_opts(parser_enter)
+    parser_enter.add_argument(
+        '--dry-run',
+        action='store_true',
+        help='print, but do not execute, the command to enter the container')
     parser_enter.add_argument(
         'command', nargs=argparse.REMAINDER,
         help='command')
@@ -4818,6 +4832,10 @@ def _get_parser():
     parser_unit.add_argument(
         '--fsid',
         help='cluster FSID')
+    parser_unit.add_argument(
+        '--dry-run',
+        action='store_true',
+        help='print, but do not execute, the unit command')
     _name_opts(parser_unit)
 
     parser_unit_install = subparsers.add_parser(
@@ -4835,6 +4853,10 @@ def _get_parser():
         '--fsid',
         help='cluster FSID')
     _name_opts(parser_logs)
+    parser_logs.add_argument(
+        '--dry-run',
+        action='store_true',
+        help='print, but do not execute, the command to show the logs')
     parser_logs.add_argument(
         'command', nargs='*',
         help='additional journalctl args')