test/lib/conds: use `:` to concatenate trigger name suffix

test/lib/conds: use `:` to concatenate trigger name suffix

For cosmetic (and obviously subjective reasons), use `:` when
appending a trigger name suffix.

Example:

    -message-iterator-class-next-method:clock-class-is-expected-mii-mii
    +message-iterator-class-next-method:clock-class-is-expected:mii-mii

I like it because it's now of the form:

    <function name>:<cond id>:<suffix>

... where the suffix discriminates different triggers to reach the
pre/post condition identified by `<function name>:<cond id>`.  When the
suffix is concatenated using `-`, it's not clear where the cond id ends.

Change-Id: I9e27524a589f19094eb90543d500d015a985a123
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12779
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>