Handle bad_generator and case_clause in ken_server

[jiahuili430]

Overview

Error log:

exit value:#012{
  {bad_generator, {nodedown,<<"progress not possible">>}},
  [
    {ken_server,'-update_db_indexes/2-lc$^0/1-0-',1,[{file,"src/ken_server.erl"},{line,272}]},
    {ken_server,update_db_indexes,2,[{file,"src/ken_server.erl"},{line,272}]}
  ]
}#012

exit value:#012{
  {case_clause,{error,{nodedown,<<"progress not possible">>}}},
  [{ken_server,update_db_indexes,2,[{file,"src/ken_server.erl"},{line,270}]}]
}#012

Testing recommendations

Related Issues or Pull Requests

Checklist

• Code is written and works correctly
• Changes are covered by tests
• Any new configurable parameters are documented in rel/overlay/etc/default.ini
• Documentation changes were made in the src/docs folder
• Documentation changes were backported (separated PR) to affected branches