Restore old argv behaviour which was lost with rc_TESTING.

The first argv deriving from cmdline will be used for all
remaining executables. Sucky semantics, but while we're in
limbo, we're in limbo, and not much sense can be made here.

Support pipe between multibaked executables.

The usual multibake cautions apply due to the currently shared
libc state, and especially in this case shared stdio state.

Allow config entries in nested objects.

Fix rc object processing.

Don't accept pipe runmode for now.

Implementing it is a bit more difficult than imagined ...

Perform some config sanity checks

rumprun_config_path: extern -> static

g/c deconfig

Should be and (mostly is) implemented by the rump kernel.

Automatically detect type of block devices in runtime config.

In other words, do not run blkid in rumprun. This change addresses
two issues:
1) systems which do not have blkid will now work
2) identifying fs type at launchtime does not do anything useful

Use rumprun_exec for the old-style cmdline passing.

(temporary compat)

Don't assign const char * to char *

Rename librumprun_base/rumpconfig.c -> config.c

"rumpconfig" is definitely the wrong name. It could be
rumprun_config.c, but let's drop the redudancy wrt. the lib name.