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.
Before my change, the sets of variables describing the JVM params were initiated before the user prompts (_1GB_master, _512MB_gc etc......).  However, the JVM settings for the 3GB tservers contains GC settings which depend on JVM vendor. So I had to put the JVM choice before setting the 3GB model. In theory, the JVM vendor could influence other variables of other processes in the future.

So this could be worded differently - the initiation of the process specific JVM parameters are now being done after the user prompts, instead of before.

Is that good enough reason to leave as is?