VM does not handle SIGQUIT during initialization

In early stage of initialization, HotSpot doesn't handle SIGQUIT. The default signal preposition on Linux is to quit the process and generate coredump.

There are 2 applications for this signal.
1. There's a handshake protocol between sun.tools.attach and HotSpot. VirtualMachineImpl sends SIGQUIT(3) if the AttachListener has not been initialized. It expects "Signal Dispatcher" to handle SIGQUIT and create AttachListener.
2. POSIX systems use SIGQUIT as SIGBREAK. After AttachListener is up, HotSpot will reinterpret the signal for thread dump.

It is possible that HotSpot is still initializing in Threads::create_vm() when SIGQUIT arrives. We should change JVM_HANDLE_XXX_SIGNAL to catch SIGQUIT and ignore it. It is installed os::init_2() and should cover the early stage of initialization. Later on, os::initialize_jdk_signal_support() still overwrites the signal handler of SIGQUIT if ReduceSignalUsage is false(default).