[ELF][test] Rewrite st_value=0 copy relocation tests

The original tests have unneeded symbols and copy-relocation-zero-abs-addr.s
does not actually test anything.

Rewrite them and add copy-relocation-zero-addr.s instead.

Add --soname=b so that the address 0x203400 will be stable.  (When linking an
executable with %t.so, the path %t.so will be recorded in the DT_NEEDED entry if
%t.so doesn't have DT_SONAME. .dynstr will have varying lengths on different
systems.)