Exit with error if any pact push operations fail

[dantb]

This affects pactPush and pactPublish. Just a suggestion really - it should maybe be considered a breaking change.

Motivation for this is that someone in our team whose name rhymes with spaniel accidentally deleted the pact.sbt for a service so the build wasn't publishing pacts for 2 months. Luckily none of its pacts were changed in that time. No-one noticed as you get this logged but the pactPublish command exits happily -

Validation error
Pact broker address not set, you need to add the following line to you SBT file:
pactBrokerAddress := "http://pactbroker.myserver.com"

[davesmith00000]

Lets review this change in the morning, looks like it's probably fine but I'd like to read it with fresh eyes.