Move to virqemu and rename to virQEMUBuildBufferEscapeComma. This can then
be shared by the storage driver when it builds the command line for qemuimg

Move the module from qemu_command.c to a new module virqemu.c and
rename the API to virQEMUBuildObjectCommandline.

This API will then be shareable with qemu-img and the need to build
a security object for luks support.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>