Make gdb.server/solib-list.exp work for remote targets

Make gdb.server/solib-list.exp work for remote targets

There are a few small changes needed to make it work with a real remote
target.

 - Remove the [is_remote target] check.
 - Remove soname setting when building the lib, it's done by default now
   anyway.
 - In the compilation of the executable, pass the shared lib using the
   shlib option, so that RPATH is set.
 - Download the program to the target using gdb_remote_download, and
   record the remote path.  Remove loading of the program using
   gdb_load_shlibs, which was not really appropriate anyway.
 - Run the remote path through readlink (see comment in the code).
 - Start gdbserver with the remote path.

Also, don't set executable and objfile variables, as they are unused.

Tested with native, native-gdbserver, native-extended-gdbserver, and a
remote gdbserver.

gdb/testsuite/ChangeLog:

	* gdb.server/solib-list.exp: Remove is_remote check.
	Pass shlib= to gdb_compile.  Don't link shared library with
	-soname.  Call gdb_remote_download instead of gdb_load_shlibs.
	Run binary filename through "readlink -f" on the target.