Fixes #416 The problem of multiple keys in ConfigWatch

[takeseem]

for multiple configurations, generally the first one is the main configuration.
so only the first configuration needs to be watch, the other will wait 1 second.
(if waitTime=0, will wait 5 minutes)

contextIndex is order itself.
It's init in ConsulPropertySourceLocator.locate(Environment environment)

for (String propertySourceContext : this.contexts) { ConsulPropertySource propertySource = sources.createPropertySource(propertySourceContext, true, this.consul, contextIndex::put); if (propertySource != null) { composite.addPropertySource(propertySource);	} }