paper: Fix boolean flag always return true

[harrisonablack]

Bug in the scripts/start-deployPaper script

When checking if we pass the --clean-libraries flag, we check if the var $CLEAN_SERVER_LIBRARIES is set

Previously this was checked by

if [[ $CLEAN_SERVER_LIBRARIES ]]; then
  args+=(--clean-libraries)
fi

However performing the test operator [[ on a variable will only return false if the variable is empty, not if it is "false". e.g.

[[ true ]]  # true
[[ false ]] # true
[[ "" ]].   # false

Fix replaces test operator with isTrue $CLEAN_SERVER_LIBRARIES, utilising isTrue function from scripts/start-utils

[itzg]

Ah yep