Add test for guest-get-osinfo command.

Qemu-ga was modified to accept QGA_OS_RELEASE environment variable. If
the variable is defined it is interpreted as path to the os-release file
and it is parsed instead of the default paths.

Signed-off-by: Tomáš Golembiovský <tgolembi@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
* move declarations to beginning of functions
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>