deploy: Rework kernel arguments, add --karg-append to "admin deploy"

The "ordered hash" code was really just for kernel arguments.  And it
turns out it needs to be a multihash (for e.g. multiple console=
arguments).

So turn the OstreeOrderedHash into OstreeKernelArgs, and move the bits
to split key=value and such into there.

Now we're not making this public API yet - the public OstreeSysroot
just takes char **kargs.  To facilitate code reuse between ostree/ and
libostree/, make it a noinst libtool library.  It'll be duplicated in
the binary and library, but that's OK for now.  We can investigate
making OstreeKernelArgs public later.

https://bugzilla.gnome.org/show_bug.cgi?id=721136

src/libostree/ostree-sysroot.h

@@ -71,15 +71,15 @@ gboolean ostree_sysroot_write_deployments (OstreeSysroot     *self,
                                            GCancellable      *cancellable,
                                            GError           **error);
 
-gboolean ostree_sysroot_deploy_one_tree (OstreeSysroot     *self,
-                                         const char        *osname,
-                                         const char        *revision,
-                                         GKeyFile          *origin,
-                                         char             **add_kernel_argv,
-                                         OstreeDeployment  *provided_merge_deployment,
-                                         OstreeDeployment **out_new_deployment,
-                                         GCancellable      *cancellable,
-                                         GError           **error);
+gboolean ostree_sysroot_deploy_tree (OstreeSysroot     *self,
+                                     const char        *osname,
+                                     const char        *revision,
+                                     GKeyFile          *origin,
+                                     OstreeDeployment  *provided_merge_deployment,
+                                     char             **override_kernel_argv,
+                                     OstreeDeployment **out_new_deployment,
+                                     GCancellable      *cancellable,
+                                     GError           **error);
 
 OstreeDeployment *ostree_sysroot_get_merge_deployment (OstreeSysroot     *self,
                                                        const char        *osname);