6490395: G1: Tidy up command line flags.
Summary: Change G1 flag names to be more consistent and disable some in 'product' mode.
Reviewed-by: tonyp, iveresov
^build/
^dist/
^nbproject/private/
^src/share/tools/hsdis/build/
^src/share/tools/IdealGraphVisualizer/[a-zA-Z0-9]*/build/
^src/share/tools/IdealGraphVisualizer/build/
^src/share/tools/IdealGraphVisualizer/dist/