JAVA_TOOL_OPTIONS environment variable

Tool vendors need a uniform mechanism for adding options to a launch of the VM.
Particularly, they need a mechanism whereby they can launch agents (such as a
JVMTI agent) along with the VM, even if the VM is embedded.

We currently prepend a _JAVA_OPTIONS environment variable but this is not
documented or supported. Since it is not standardized, other vendors have
their own names e.g. IBM_JAVA_OPTIONS. Leading underscore names are private
so we don't want to standardize _JAVA_OPTIONS additionally it doesn't match
functionality we want to standardize, for example it doesn't support qoutes.
So we need a new name and it should indicate it's intended usage so slightly
lessen the likelyhood of misuse -- JAVA_TOOL_OPTIONS.