Introduce vm.verify_userspace_crash()

In order to capture any qemu crashes, introduce a method
that scans qemu output and throws an error if a core dump
condition is found.

Improve verify_alive() by calling this function, among
others, and add a check on two of the most called functions
of the framework: vm.wait_for_login() and
vm.wait_for_serial_login().
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

tests/unattended_install.py

@@ -827,7 +827,6 @@ def run_unattended_install(test, params, env):
                 break
             else:
                 raise e
-        vm.verify_kernel_crash()
         test.verify_background_errors()
         finish_signal = vm.serial_console.get_output()
         if (params.get("wait_no_ack", "no") == "no" and