The function would generate a leading comma. Let the callers properly
add commas by formatting the commas at the end and trimming the trailing
one.

For use with memory hotplug virQEMUBuildCommandLineJSONRecurse attempted
to format JSON arrays as bitmap on the command line. Make the formatter
function configurable so that it can be reused with different syntaxes
of arrays such as numbered arrays for use with disk sources.

This patch extracts the code and adds a parameter for the function that
will allow to plug in different formatters.

Move the iterator of objects to the recursive function so that nested
objects are supported by flattening the structure with '.' delimiters.

Until now the JSON->commandline convertor was used only for objects
created by qemu. To allow reusing it with disk formatter we'll need to
escape ',' as usual in qemu commandlines.

Refactor the command line generator by adding a wrapper (with
documentation) that will handle the outermost object iteration.

This patch also renames the functions and tweaks the error message for
nested arrays to be more universal.

The new function is then reused to simplify qemucommandutiltest.

Partially resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=1301021

If the volume xml was looking to create a luks volume take the necessary
steps in order to make that happen.

The processing will be:
 1. create a temporary file (virStorageBackendCreateQemuImgSecretPath)
   1a. use the storage driver state dir path that uses the pool and
       volume name as a base.

 2. create a secret object (virStorageBackendCreateQemuImgSecretObject)
   2a. use an alias combinding the volume name and "_luks0"
   2b. add the file to the object

 3. create/add luks options to the commandline (virQEMUBuildLuksOpts)
   3a. at the very least a "key-secret=%s" using the secret object alias
   3b. if found in the XML the various "cipher" and "ivgen" options
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

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>