AMICA on Linux (non Expanse)

[tiborauer]

Issue: amica15ub is never selected, and amica15ex is used for any Linux system
https://github.com/japalmer29/amica/blob/ffbcc10fe8527b5e5c662a8af6b622d3ab26d4c6/runamica15.m#L99-L106

Solution: make amica15ub default for Linux systems, and select amica15ex only when Expanse is detected.