RFR: Improve assertion/verification messages a bit

[Roman Kennke]

Ok

On Wed, Feb 14, 2018 at 5:01 PM, Aleksey Shipilev <shade at redhat.com> wrote:
> http://cr.openjdk.java.net/~shade/shenandoah/verifier-print-clean/webrev.01/
>
> Cleans up assertion/verification messages a bit: missing/excessive new lines, messages, punctuation.
>
> Testing: hotspot_fast_gc_shenandoah, eyeballing injected failures
>
> -Aleksey
>