s2pexec: Return sense key and ASC as exit status

[uweseimet]

In order to improve scripting support s2pexec shall return the error status of a command as exit status. The meaning of the exit status:

• 0: No error
• -1: General error, e.g. target does not exist
• Any other value: The lowest 16 bit of the exit status are the sense key (upper 8 bit) and the ASC (lower 8 bit)

[uweseimet]

The exit status only has 8 bits, i.e. it cannot represent both sense key and ASC. Thus only the ASC value will be used.