Platform/Intel/Tools: Add scripts to set PACKAGES_PATH environment

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2656



1. Add GetPackagesPath.py, it will be used to get package pathes from
  special directories. A sub directory is a qualified package path
  when an EDKII Package can be found under it.
2. Add AppendPackagesPath.bat and AppendPackagesPath.sh, these scripts
  call GetPackagesPath.py to collect all package paths under specified
  directories and append them to PACKAGES_PATH environment variable.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Amy Chan <amy.chan@intel.com>
Signed-off-by: Heng Luo <heng.luo@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>