crimson: pass entity_name and cluster to ctor of ConfigProxy

crimson: pass entity_name and cluster to ctor of ConfigProxy

as we always need to set entity_name and cluster before start using
ConfigProxy, and we do not read these settings from config file,
this makes these two setting special. so it'd be simpler to just
pass them as parameters of constructor.

and more importantly, we need to parse the command line arguments
using ceph_argparse_early_args() first, as it will consume the parsed
arguments, and leave the unparsed ones in the input parameter of `args`,
and then, we can pass the unparsed args to app.run().

it's not a perfect solution. as there are some options that both parsers
are interested, for instance, `-c` -- ceph take it as the conf file's
path, while seastar takes it as the number of cores to use. but let's
feed ceph's parser first. unless it's fine to drop the backward
compatibility of command line syntax of ceph-osd.

Signed-off-by: Kefu Chai <kchai@redhat.com>
Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>