BaseTools/edksetup.sh: fix invalid test for current working directory

BaseTools/edksetup.sh: fix invalid test for current working directory

edksetup.sh implements a test that requires the current working
directory to contain the edksetup.sh script.  This test has the side
effect of requiring the WORKSPACE to be set to the same directory as
the edksetup.sh.  In a multiple workspace configuration, it is
required to be able to have a WORKSPACE that is different from the
directory that contains edksetup.sh.  This changeset skips this test
if PACKAGE_PATH is set.

Change-Id: Ie6f16a08c012baf4e650c48cc8e91cdc466d05f2
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chris Ruffin <chris.ruffin@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>