BUG/MINOR: check: Update server address and port to execute an external check

BUG/MINOR: check: Update server address and port to execute an external check

Server address and port may change at runtime. So the address and port passed as
arguments and as environment variables when an external check is executed must
be updated. The current number of connections on the server was already updated
before executing the command. So the same mechanism is used for the server
address and port. But in addition, command arguments are also updated.

This patch must be backported to all stable versions. It should fix the
issue #577.