qemu: command: Fix building of the SDL display command line

qemu: command: Fix building of the SDL display command line

QEMU uses a shorthand '-sdl' which maps to '-display sdl'. However, if
there are any options to be passed to SDL, the full command version must
be used. Everything seemingly worked for us until commit 5038b300437
introduced OpenGL support for SDL and added ',gl=on/off' option which as
mentioned above could have never worked with the shorthand version of
the command. Indeed starting a domain with an SDL display and OpenGL
enabled, QEMU produces a rather cryptic error:

-sdl: Could not open 'gl=on': No such file or directory

This patch provides fixes to both the SDL cmdline generation and the
test suite.

Signed-off-by: Erik Skultety <eskultet@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>