Fixes harded coded Sun JVM in config and env

ACCUMULO-2944 add support for multiple java vendors in conf & scripts

Support for multiple java vendors is added by getting the
bootstrap_config.sh to generate correct configuration depending on 
specified java vendor. Following details depend on Java vendor

* GC settings
* Exclude/Include JAXP implementation
* Default NRG provider

 
A new question is being asked in the bootstrap_config.sh for Java 
vendor. This is then used to set GC settings, exclude/include JAXP 
implementation in ACCUMULO_OPTS. Also, default NRG provider is being 
injected as system property on command line since IBM JVM does not 
have SUN registered as default provider.
That sounds like a good reason to move the user prompts up to before all the initialization.