ShellPkg: Update MV.  now supports across file system moves.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Erik Bjorge <erik.c.bjorge@intel.com>
Reviewed-by: Tapan Shah <tapandshah@hp.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16193 6f19259b-4bc3-4df7-8a09-765794883524
ShellPkg: Update SetVar to use existing attributes for updating existing variables.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Erik Bjorge <erik.c.bjorge@intel.com>
Reviewed-by: Tapan Shah <tapandshah@hp.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16194 6f19259b-4bc3-4df7-8a09-765794883524