main: hide --failover CLI option

The failover agent is not ready at the moment. Let's hide the CLI option
from the help message, but still handle it: it is useful to continue the
development of the agent.

See tarantool/tarantool-ee#564

NO_DOC=The option is not present into the documentation.
NO_CHANGELOG=No behavior changes, just help message.

doc/man/tarantool.pod

@@ -148,12 +148,6 @@ option (as a modifier).
 
 Run the interactive REPL.
 
-=item --failover
-
-Run a failover coordinator service.
-
-It is available in Tarantool Enterprise Edition.
-
 =back
 
 =head2 MODIFIER OPTIONS

src/main.cc

@@ -697,12 +697,6 @@ print_help(FILE *stream)
 		"\n"
 		"    Run the interactive REPL.\n"
 		"\n"
-		"--failover\n"
-		"\n"
-		"    Run a failover coordinator service.\n"
-		"\n"
-		"    It is available in Tarantool Enterprise Edition.\n"
-		"\n"
 		"The following modifier options are applicable to actions.\n"
 		"\n"
 		"--force-recovery\n"

test/box-py/args.result

@@ -71,12 +71,6 @@ At the lower level there are the following action options.
 
     Run the interactive REPL.
 
---failover
-
-    Run a failover coordinator service.
-
-    It is available in Tarantool Enterprise Edition.
-
 The following modifier options are applicable to actions.
 
 --force-recovery
@@ -188,12 +182,6 @@ At the lower level there are the following action options.
 
     Run the interactive REPL.
 
---failover
-
-    Run a failover coordinator service.
-
-    It is available in Tarantool Enterprise Edition.
-
 The following modifier options are applicable to actions.
 
 --force-recovery