Add new function to manage adding the -fsdev options to the
command line removing that task from the mainline qemuBuildCommandLine.
Alter the code slightly to perform the !caps and fsdev failure check
up front.

Since both qemuBuildFSStr and qemuBuildFSDevStr are local, make them
static and fix their prototypes to use the const virDomainDef as well.
Make some minor formatting changes for long lines.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>