Move .stxxl file into index directory

[lehmann-4178656ch]

When the .stxxl file is generated where the binaries are stored some docker setups (related to --user/userns) can result in the following error:

IndexBuilderMain, version Apr 25 2019 10:35:41

Set locale LC_CTYPE to: C.UTF-8
Thu May  9 09:45:38.627	- DEBUG: Configuring STXXL...
terminate called after throwing an instance of 'std::runtime_error'
  what():  ! ERROR opening file ".stxxl" with mode "w" (Permission denied)

This pullrequest changes the location of the .stxxl file to reside in the index directory next to the disk file so write permissions there hopefully suffices to run the respective binaries.

[niklas88]

Sadly STXXL is hard coded to search in the current directory and ~ see here. This means that this change results in the defaults being used and not the index/.stxxl file

[lehmann-4178656ch]

Now the correct path (and config) /app/e2e_data/scientists-index-stxxl.disk is used instead of the default stxxl config /var/tmp/foxxll

[niklas88]

LGTM