ctf: Add dash to stream name suffixes

We add numerical suffixes to stream names, if needed, to make them
unique. For trace directories, we do something similar and decided to
format these suffixes with a dash to avoid confusion if the original
name ends with a number.  This patch does the same thing but for stream
names.

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Change-Id: I3041fe98bbeb3c122d06e5fa54449ed6e55017bd
Reviewed-on: https://review.gerrithub.io/c/eepp/babeltrace/+/452110
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: Philippe Proulx <eeppeliteloop@gmail.com>