ShellPkg/Shell: Fix reporting of exit status in ShellProtocol.Execute

ShellPkg/Shell: Fix reporting of exit status in ShellProtocol.Execute

When the exit status of the command run by the shell is other than
SHELL_SUCCESS, the shell image will now exit with EFI_ABORTED, placing the
commands exit status (which is a SHELL_STATUS) in ExitData.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Brendan Jackman <Brendan.Jackman@arm.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Jaben Carsey <Jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15180 6f19259b-4bc3-4df7-8a09-765794883524