Improve the error handling of qemu start

[coolo]

Before:

13:59:23.1513 9572 starting: /usr/bin/qemu-kvm -serial file:serial0 -soundhw ac97 -global isa-fdc.driveA= -vgas cirrus -m 1024 -netdev user,id=qanet0 -device virtio-net,netdev=qanet0,mac=52:54:00:12:34:56 -device virtio-scsi-pci,id=scsi0 -device virtio-blk,drive=hd1 -drive file=raid/l1,cache=unsafe,if=none,id=hd1,format=qcow2 -boot once=d,menu=on,splash-time=5000 -device usb-ehci -device usb-tablet -smp 1 -enable-kvm -no-shutdown -vnc :103,share=force-shared -qmp unix:qmp_socket,server,nowait -monitor unix:hmp_socket,server,nowait -S -monitor telnet:127.0.0.1:20132,server,nowait
13:59:25.1067 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:26.1075 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:27.1083 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:28.1091 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:29.1099 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:30.1106 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:31.1113 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
13:59:32.1121 9566 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
DIE Can't locate object method "blessed" via package "socket does not exist. Probably your backend instance could not start or died. at /suse/coolo/prod/os-autoinst/consoles/VNC.pm line 879.
" (perhaps you forgot to load "socket does not exist. Probably your backend instance could not start or died. at /suse/coolo/prod/os-autoinst/consoles/VNC.pm line 879.
"?) at /suse/coolo/prod/os-autoinst/consoles/VNC.pm line 794.

 at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 73.
        backend::baseclass::die_handler("Can't locate object method \"blessed\" via package \"socket does"...) called at /suse/coolo/prod/os-autoinst/consoles/VNC.pm line 794
        consoles::VNC::catch {...} ("socket does not exist. Probably your backend instance could n"...) called at /usr/lib/perl5/vendor_perl/5.24.0/Try/Tiny.pm line 124
        Try::Tiny::try(CODE(0x52ebac0), Try::Tiny::Catch=REF(0x1361778)) called at /suse/coolo/prod/os-autoinst/consoles/VNC.pm line 801
        consoles::VNC::update_framebuffer(consoles::VNC=HASH(0x53d43d0)) called at /suse/coolo/prod/os-autoinst/consoles/vnc_base.pm line 68
        consoles::vnc_base::request_screen_update(consoles::vnc_base=HASH(0x52a4ab8)) called at /suse/coolo/prod/os-autoinst/consoles/vnc_base.pm line 80
        consoles::vnc_base::current_screen(consoles::vnc_base=HASH(0x52a4ab8)) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 573
        backend::baseclass::capture_screenshot(backend::qemu=HASH(0x41d7eb8)) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 468
        backend::baseclass::select_console(backend::qemu=HASH(0x41d7eb8), HASH(0x34b3610)) called at /suse/coolo/prod/os-autoinst/backend/qemu.pm line 786
        backend::qemu::start_qemu(backend::qemu=HASH(0x41d7eb8)) called at /suse/coolo/prod/os-autoinst/backend/qemu.pm line 101
        backend::qemu::do_start_vm(backend::qemu=HASH(0x41d7eb8)) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 252
        backend::baseclass::start_vm(backend::qemu=HASH(0x41d7eb8), undef) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 68
        backend::baseclass::handle_command(backend::qemu=HASH(0x41d7eb8), HASH(0x52a4878)) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 422
        backend::baseclass::check_socket(backend::qemu=HASH(0x41d7eb8), IO::Handle=GLOB(0x4fe5de8)) called at /suse/coolo/prod/os-autoinst/backend/qemu.pm line 1006
        backend::qemu::check_socket(backend::qemu=HASH(0x41d7eb8), IO::Handle=GLOB(0x4fe5de8), 0) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 203
        eval {...} called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 151
        backend::baseclass::run_capture_loop(backend::qemu=HASH(0x41d7eb8)) called at /suse/coolo/prod/os-autoinst/backend/baseclass.pm line 122
        backend::baseclass::run(backend::qemu=HASH(0x41d7eb8), 6, 9) called at /suse/coolo/prod/os-autoinst/backend/driver.pm line 85
        backend::driver::start(backend::driver=HASH(0x34b2b90)) called at /suse/coolo/prod/os-autoinst/backend/driver.pm line 48
        backend::driver::new("backend::driver", "qemu") called at /suse/coolo/prod/os-autoinst/isotovideo line 198
        main::init_backend() called at /suse/coolo/prod/os-autoinst/isotovideo line 263
13:59:33.1157 9566 waitpid for 9572 returned 9572
last frame
13:59:33.2168 9566 QEMU: qemu-system-x86_64: -vgas: invalid option
13:59:33.2171 9566 sending magic and exit

After:

14:01:14.8701 10303 starting: /usr/bin/qemu-kvm -serial file:serial0 -soundhw ac97 -global isa-fdc.driveA= -vgas cirrus -m 1024 -netdev user,id=qanet0 -device virtio-net,netdev=qanet0,mac=52:54:00:12:34:56 -device virtio-scsi-pci,id=scsi0 -device virtio-blk,drive=hd1 -drive file=raid/l1,cache=unsafe,if=none,id=hd1,format=qcow2 -boot once=d,menu=on,splash-time=5000 -device usb-ehci -device usb-tablet -smp 1 -enable-kvm -no-shutdown -vnc :103,share=force-shared -qmp unix:qmp_socket,server,nowait -monitor unix:hmp_socket,server,nowait -S -monitor telnet:127.0.0.1:20132,server,nowait
14:01:16.8257 10297 Error connecting to host <localhost>: IO::Socket::INET: connect: Connection refused
14:01:17.8270 10297 qemu didn't start
14:01:17.8289 10297 QEMU: qemu-system-x86_64: -vgas: invalid option

[coveralls]

Coverage decreased (-0.01%) to 52.059% when pulling 4b58501 on coolo:better_qemu_error into 007691c on os-autoinst:master.

[okurz]

LGTM, perfect