ldb: Use libraries from build dir for testsuite

ldb: Use libraries from build dir for testsuite

There was a failure when tests were executed after after extracting
ldb tarball.

  sh$ make -j8 check
  WAF_MAKE=1 PATH=buildtools/bin:../../buildtools/bin:$PATH waf test
  ldbadd: error while loading shared libraries: libldb.so.1: cannot open shared object file: No such file or directory
  cat: write error: Broken pipe
  Traceback (most recent call last):
    File "tests/python/api.py", line 10, in <module>
      import ldb
  ImportError: libldb.so.1: cannot open shared object file: No such file or directory
  Traceback (most recent call last):
    File "tests/python/api.py", line 10, in <module>
      import ldb
  ImportError: libpyldb-util.so.1: cannot open shared object file: No such file or directory
  bin/ldb_tdb_mod_op_test: error while loading shared libraries: libldb.so.1: cannot open shared object file: No such file or directory
  testsuite returned 1

Signed-off-by: Lukas Slebodnik <lslebodn@redhat.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Signed-off-by: Alexander Bokovoy <ab@samba.org>