select/cray: AlpsDir only used by apbasil/apkill

When using an emulated setting, the user is likely to specify both apbasil and
apkill, hence the AlpsDir variable could be refactored, which is what the patch
does. It falls back to the Cray-like defaults (/usr/bin) if nothing is set.
05_COSMETICS_Cray-conf-AlpsDir-simplification.diff from Gerrit Renker, CSCS