Exhibitor tests the auto-manage-instances config value to see if it's a
non-zero integer, rather than a true/false string, which was getting
put into the config before. This now causes autoManageInstances to
behave correctly.
The previous package didn't build properly due to a bug in the build
script, and the nixos module didn't evaluate due to missing descriptions
in the options. This fixes both issues.
It also adds missing command-line options that weren't able to be set
and properly converts bools to the strings exhibitor expects.
