command: shell-quote when logging commands

command: shell-quote when logging commands

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.