Without this patch, logged command executions can be ambiguous if
the command contained any shell metacharacters.  This has caused
more than one person to attempt to patch clients to add unnecessary
quoting, without realizing that the command itself was run with
correct args, and only the logged output was ambiguous.

* src/util/command.c (virCommandToString): Add shell escapes.
* tests/commandtest.c (test16): Test new behavior.
* tests/commanddata/test16.log: Update expected output.
* tests/qemuxml2argvdata/qemuxml2argv-*.args: Likewise.
* tests/networkxml2argvdata/*.argv: Likewise.

This patch teaches testutil how to read multi-line input files with
backspace-newline line continuation markers.

The patch also breaks up all the single-line arguments test input files into
multi-line files with lines shorter than 80 characters.

Thanks to DV for knocking together the Relax-NG changes
quickly for me.

Changes since v1:
 - Change the domain.rng to correspond to the new schema
 - Don't allocate caps->ns in testQemuCapsInit since it is a static table

Changes since v2:
 - Change domain.rng to add restrictions on allowed environment names

Changes since v3:
 - Remove a bogus comment in the tests
Signed-off-by: NChris Lalancette <clalance@redhat.com>