Fixes harded coded Sun JVM in config and env

Addressing the issue raised in JIRA 2944, this is ensuring that
Accumulo will be correctly configured for any Java vendor.

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.