bhyvexml2argvtest: Use internal wrapping of command line arguments

bhyvexml2argvtest: Use internal wrapping of command line arguments

virCommandToString has the possibility to return an already wrapped
string with better format than what we get from the test wrapper script.

The main advantage is that arguments for an option are always on the
same line which makes it more easy to see what changed in a diff and
prevents re-wrapping of the line if a wrapping point moves over the
threshold.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>